Short answer. The shares are reduced proportionally. Article 853 of the Civil Code provides that if the aliquot parts given to the instituted heirs together exceed the whole inheritance, each part shall be reduced proportionally so that all shares together equal the available estate — no single heir gets priority in the reduction.
What the law says
If each of the instituted heirs has been given an aliquot part of the inheritance, and the parts together exceed the whole inheritance, or the whole free portion, as the case may be, each part shall be reduced proportionally.
Civil Code, Article 853 — Shares Reduced Proportionally. Read the full provision →
The proportional reduction rule
Article 853 of the Civil Code addresses a specific drafting problem in testamentary succession: when the testator assigns fractional shares to multiple heirs and the fractions add up to more than the available estate. The rule is clear: If each of the instituted heirs has been given an aliquot part of the inheritance, and the parts together exceed the whole inheritance, or the whole free portion, as the case may be, each part shall be reduced proportionally. No heir is favored in the reduction. All shares are cut back at the same rate so that together they fit within what is actually available.
How proportional reduction works in practice
Proportional reduction preserves the relative sizes of the heirs' shares as the testator intended them, while scaling all shares down to fit the estate. If three heirs were given 50%, 40%, and 30% respectively — a total of 120% — each fraction is divided by the total (1.2) to produce adjusted shares of approximately 41.7%, 33.3%, and 25%. The heirs' proportional relationship to each other remains the same as what the testator specified; only the absolute percentages change. The heir with the largest share still gets the most, the smallest share still gets the least, and all shares together now equal exactly the whole estate.
Applies to the free portion as well
Article 853 addresses not only situations where the assigned shares exceed the whole inheritance, but also situations where they exceed the whole free portion. In Philippine succession law, the estate is divided between the legitime — reserved by law for compulsory heirs — and the free portion, which the testator can dispose of as they wish. If the testator assigned shares out of the free portion that together exceed what is actually available in that portion, the same proportional reduction applies. The reduction operates within whichever relevant pool of assets has been over-allocated.
Practical implications for the heirs
For the heirs in your father's estate, the correction does not require a court to declare the will partially void or to choose which heir receives less. The law itself provides the mechanism: reduce each share proportionally. The heirs and the administrator can apply Article 853's rule directly in computing the distribution. Each heir receives a smaller absolute share than what the will states, but the relative ranking among heirs — who gets more and who gets less — is preserved exactly as the testator intended. This is a practical, fair correction to a common drafting error that avoids giving any heir an unfair advantage in the reduction.