A sale by a co-owner of the entire co-owned property is valid only with respect to the seller's pro-indiviso share, and the sale of the shares of other co-owners without their authority or legal representation is unenforceable; mere silence or inaction of such other co-owners, without proof of their awareness of the unauthorized sale and a voluntary, knowing adoption of the act, does not constitute ratification.

The subject property, consisting of two parcels of land (Cadastral Lots Nos. 5737 and 5738) in Sta. Monica, Hagonoy, Bulacan, was originally owned by Honoria Aguinaldo. Upon Honoria's death, one-half (1/2) of the property was inherited by petitioner Emilia Meking Vda. de Coronel together with her sons, petitioner Benjamin, Catalino, and Ceferino, all surnamed Coronel. The other half was inherited by respondents Florentino Constantino and Aurea Buensuceso. The dispute arose from the sale of the portion inherited by Emilia and her sons.

• The subject property was co-owned by petitioner Emilia Meking Vda. de Coronel and her three sons: petitioner Benjamin, Catalino, and Ceferino. This group collectively owned one-half (1/2) of the entire property, inherited from Honoria Aguinaldo.
• On April 23, 1981, Emilia executed a private document, "Kasulatan ng Bilihang Patuluyan," purportedly selling their co-owned portion to Jess C. Santos and Priscilla Bernardo for P25,000.
• The "Kasulatan" was signed by Emilia as seller ("Nagbili") and by Jess C. Santos and Priscilla Bernardo as buyers ("Nakabili"). Benjamin M. Coronel was named as a seller ("Nagbili") in the document, but his signature space was unsigned.
• On June 21, 1990, Jess C. Santos and Priscilla Bernardo sold the same property to respondents Florentino Constantino and Aurea Buensuceso via a compromise agreement in Civil Case No. 8289-M.
• Respondents Constantino and Buensuceso then filed a complaint against Emilia and Benjamin, claiming ownership and alleging illegal construction by the Coronels.
• During pre-trial, counsel for the Coronels admitted that Emilia signed the "Kasulatan ng Bilihang Patuluyan."
• Catalino Coronel died in 1983, and Ceferino Coronel died in 1990. Their shares were also purportedly included in the sale by Emilia.

• The contract of sale ("Kasulatan ng Bilihang Patuluyan") executed by Emilia is unenforceable with respect to the shares of her co-heir children (Benjamin, Catalino, and Ceferino) because she had no authority to sell their respective shares.
• The children, particularly Benjamin, Catalino, and Ceferino, did not ratify the unauthorized sale of their shares by their mother, Emilia.
• The heirs of Catalino and Ceferino, who died prior to or during the litigation, are indispensable parties to the action for declaration of ownership and quieting of title, and their non-impleader should have resulted in the dismissal of the complaint.
• The private deed of sale was not sufficiently established as evidence of a valid transfer of the children's shares, as the admission by counsel only pertained to Emilia's signature, not the binding effect of its contents on the children.
• Emilia claimed she signed the "Kasulatan" under the mistaken belief that it was a contract of mortgage, not a deed of sale.

• They are the lawful owners of the disputed portion of the property, having acquired it through a valid sale from Jess C. Santos and Priscilla Bernardo, who in turn validly purchased it from Emilia Meking Vda. de Coronel.
• The sale by Emilia, even if initially unauthorized concerning her children's shares, was subsequently ratified by the children (Benjamin, Catalino, and Ceferino) through their prolonged inaction and silence, as determined by the Court of Appeals.
• The due execution of the "Kasulatan ng Bilihang Patuluyan" by Emilia was sufficiently established by the admission of petitioners' counsel during the pre-trial conference.
• (Implicitly, by defending the lower courts' decisions) The heirs of Catalino and Ceferino were not indispensable parties, or any objection to their non-joinder was waived by the petitioners.

• Whether the contract of sale executed by Emilia Meking Vda. de Coronel, a parent-co-owner, in her own behalf, is unenforceable with respect to the shares of her co-heirs-children (Benjamin, Catalino, and Ceferino).
• Whether minor children (or co-heirs generally) can be deemed to have ratified the unauthorized sale of their property shares by their parent through inaction or silence.
• Whether the co-heirs (specifically, the heirs of the deceased Catalino and Ceferino) are indispensable defendants in an action for declaration of ownership and quieting of title concerning the co-owned property.
• Whether the deed of sale, being a private document, was sufficiently established as to its binding effect on all named sellers when counsel for petitioners admitted only Emilia's signature but not its contents as affecting the children's shares.

• The Supreme Court AFFIRMED the decision of the Court of Appeals WITH MODIFICATIONS.
• The sale made by Emilia Meking Vda. de Coronel to Jess C. Santos and Priscilla Bernardo is VALID only with respect to Emilia's one-fourth (1/4) pro-indiviso share of the one-half (1/2) portion of the subject property co-owned with her sons. The sale is UNENFORCEABLE with respect to the shares of Benjamin, Catalino, and Ceferino, as Benjamin did not sign the deed, and Emilia had no authority or legal representation to dispose of her sons' shares.
• There was NO RATIFICATION by Benjamin, Catalino, and Ceferino of the sale of their respective shares. The Court found no evidence that the sons were aware of the sale made by their mother or that they knowingly and voluntarily chose not to annul it. Their alleged silence and inaction, without proof of knowledge and intent, do not constitute ratification. There was also no proof that they benefited from the proceeds of the sale.
• The heirs of Catalino and Ceferino Coronel are NOT INDISPENSABLE PARTIES to the present case. Since their shares were not validly sold, a complete determination of the rights between petitioners (Emilia and Benjamin) and respondents (Constantino and Buensuceso) regarding Emilia's sold share and Benjamin's unsold share could be achieved without impleading said heirs. Moreover, petitioners were estopped from raising this issue for the first time on appeal after actively participating in the trial court proceedings without objection.
• The due execution of the "Kasulatan ng Bilihang Patuluyan" by Emilia was deemed sufficiently established for her share, based on her counsel's admission during pre-trial that she signed the document. Her claim of mistake (believing it was a mortgage) was not substantiated by competent evidence.
• Consequently, respondents Constantino and Buensuceso were declared owners of the one-half (1/2) undivided portion they originally inherited, plus the one-fourth (1/4) undivided share of Emilia Meking Vda. de Coronel. Petitioner Benjamin Coronel, along with the heirs of Catalino Coronel and the heirs of Ceferino Coronel, remain co-owners of their respective one-fourth (1/4) shares each of the other one-half (1/2) portion of the subject property. The RTC's order for removal of improvements and payment of attorney's fees was DELETED.

• Co-ownership (Article 493, Civil Code) — Each co-owner has full ownership of his part and the fruits pertaining thereto, and may alienate, assign, or mortgage it, but the effect of such alienation is limited to the portion allotted to him upon division. This doctrine was applied to affirm that Emilia could only validly sell her own undivided interest in the co-owned property.
• Unenforceable Contracts (Article 1317 and Article 1403(1), Civil Code) — Article 1317 states that no one may contract in the name of another without authorization or legal representation; such contracts are unenforceable unless ratified. Article 1403(1) deems unenforceable contracts entered into in another's name by one without authority or who acted beyond his powers, unless ratified. These provisions were applied to declare the sale of the children's shares by Emilia unenforceable because she lacked their authority.
• Ratification — Defined as the voluntary adoption and sanctioning of an unauthorized act by one under no disability, which makes the previously unauthorized act binding. It requires a voluntary choice, knowingly made. The Court applied this to find no ratification by Emilia's sons, as there was no evidence of their awareness of the sale or any voluntary act to confirm it; mere silence or inaction was insufficient.
• Indispensable Parties (Rule 3, Section 7, 1997 Rules of Civil Procedure) — These are parties in interest without whom no final determination of an action can be had. The Court held that the heirs of Catalino and Ceferino were not indispensable because their shares were not deemed sold, and a complete adjudication of rights concerning Emilia's and Benjamin's shares vis-a-vis the respondents was possible without them.
• Estoppel by Laches (in relation to jurisdictional challenges) — A party may be barred from raising a jurisdictional issue, such as the non-joinder of indispensable parties, if they participated in trial court proceedings without raising the issue and only do so on appeal. This doctrine estopped petitioners from challenging the trial court's jurisdiction on this ground.
• Bare Allegations are Not Proof — Mere assertions unsubstantiated by evidence do not constitute proof under the Rules of Court. This was applied to disregard respondent Constantino's uncorroborated testimony that Benjamin benefited from the sale.

• "Ratification means that one under no disability voluntarily adopts and gives sanction to some unauthorized act or defective proceeding, which without his sanction would not be binding on him. It is this voluntary choice, knowingly made, which amounts to a ratification of what was theretofore unauthorized, and becomes the authorized act of the party so making the ratification."
• "No evidence was presented to show that the three brothers were aware of the sale made by their mother. Unaware of such sale, Catalino, Ceferino and Benjamin could not be considered as having voluntarily remained silent and knowingly chose not to file an action for the annulment of the sale. Their alleged silence and inaction may not be interpreted as an act of ratification on their part."
• "Bare allegations, unsubstantiated by evidence, are not equivalent to proof under our Rules of Court."

• Maglucot-Aw vs. Maglucot (329 SCRA 78, 94 [2000]) — Referenced for its definition of "ratification," emphasizing that it must be a voluntary and knowing act. This supported the Court's finding that Emilia's sons did not ratify the unauthorized sale of their shares.
• Bayoca vs. Nogales (340 SCRA 154, 169 [2000]) — Cited for the general rule that jurisdictional questions can be raised at any time, with the exception of estoppel. This was applied to rule that petitioners were estopped from raising the issue of non-joinder of indispensable parties late in the proceedings.
• Manzano vs. Perez, Sr. (362 SCRA 430, 439 [2001]) — Invoked for the principle that bare allegations without substantiating evidence are not equivalent to proof. This was used to dismiss the unsupported claim that Benjamin received part of the sale consideration.

• Civil Code, Article 493 — This article on co-ownership was fundamental in determining that Emilia could only alienate her own specific share, and the sale of her children's shares without their consent was ineffective against them.
• Civil Code, Article 1317 — This article, stating that a contract entered into in the name of another without authority is unenforceable unless ratified, was applied to the sale of the children's shares by Emilia.
• Civil Code, Article 1403(1) — This provision lists unenforceable contracts, including those entered into in the name of another by one who has no authority or legal representation, unless ratified. It further supported the unenforceability of the sale of the children's shares.
• 1997 Rules of Civil Procedure, Rule 3, Section 7 — This rule defining indispensable parties was used to analyze the petitioners' claim regarding the non-joinder of the heirs of Catalino and Ceferino, concluding they were not indispensable under the circumstances.