Co-ownership by all legal heirs of the estate of decedent - Each co-owner shall have the full ownership of his part and of the fruits and benefits pertaining thereto, and he may therefore alienate, assign or mortgage it, and even substitute another person in its enjoyment, except when personal rights are involved. But the effect of the alienation of the mortgage, with respect to the co-owners shall be limited to the portion which may be allotted to him in the division upon the termination of the co-ownership.

See - https://www.manilatimes.net/2020/03/18/legal-advice/dearpao/selling-a-co-owned-property/703914/


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You are also a co-owner of the property pursuant to the rule on succession. Under Article 774 of the New Civil Code of the Philippines, it is stated that:

“Succession is a mode of acquisition by virtue of which the property, rights and obligations to the extent of the value of the inheritance of a person are transmitted through his death to another or others either by his will or by operation of law.”

It is important to emphasize that you became a co-owner of the said property upon the death of your father. This is in consonance with Article 777 of the said Code, which states that “the rights to the succession are transmitted from the moment of the death of the decedent.”Corollary to the above-mentioned provisions of law is Article 493 of the same Code, which provides that:

“Each co-owner shall have the full ownership of his part and of the fruits and benefits pertaining thereto, and he may therefore alienate, assign or mortgage it, and even substitute another person in its enjoyment, except when personal rights are involved. But the effect of the alienation of the mortgage, with respect to the co-owners shall be limited to the portion which may be allotted to him in the division upon the termination of the co-ownership.”
This law was expounded by the court in the case of Philippine National Bank vs. Garcia, et al. (GR 182839, June 2, 2014), where the Supreme Court through Associate Justice Arturo Brion stated that:

“While under Article 493 of the New Civil Code, each co-owner shall have the full ownership of his part and of the fruits and benefits pertaining thereto and he may alienate, assign or mortgage it, and even substitute another person in its enjoyment, the effect of the alienation or the mortgage with respect to the co-owners, shall be limited, by mandate of the same article, to the portion which may be allotted to him in the division upon the termination of the co-ownership. He has no right to sell or alienate a concrete, specific, or determinate part of the thing in common to the exclusion of the other co-owners because his right over the thing is represented by an abstract or Ideal portion without any physical adjudication. An individual co- owner cannot adjudicate to himself or claim title to any definite portion of the land or thing owned in common until its actual partition by agreement or judicial decree. Prior to that time all that the co-owner has is an ideal or abstract quota or proportionate share in the entire thing owned in common by all the co-owners. What a co-owner may dispose of is only his undivided aliquot share, which shall be limited to the portion that may be allotted to him upon partition. xxx”

Applying the above-quoted decision in your situation, you and your siblings and your
mother became the co-owners of the land upon the death of your father. Your mother, being a co-owner, cannot dispose or sell the entire property. She can only sell her undivided aliquot share, which is limited to the portion that may be allotted to her upon partition.

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