Short answer. The widow takes one-half of the estate and the qualified brothers and sisters — with nephews and nieces standing in the place of a sibling who died ahead — divide the other half. That split only applies where neither parent of the deceased survives; if a parent survives, the parent inherits ahead of the siblings.
What the law says
If the widow or widower should survive with brothers and sisters, nephews and nieces, she or he shall inherit one-half of the estate, and the latter the other half.
Civil Code, Article 994 — Spouse of an Illegitimate Child. Read the full provision →
The order the Civil Code sets
The rule is a ladder, and the widow's share depends on which rung is occupied. The parents of the deceased come first: the spouse of an illegitimate child inherits in default of the father or mother. If a parent survives and filiation to that parent is proved, the spouse does not take the whole estate. Where no parent survives and there are also no brothers, sisters, nephews or nieces, the surviving spouse is entitled to the entire estate. It is only where the widow or widower survives alongside qualified siblings, nephews or nieces that the estate is halved between them. Descendants of the deceased, if any, would displace all of this.
How this article reads today
The share above was worked out on the classification of children that applied when the Civil Code took effect in 1950, and it must now be read subject to the Family Code. The Family Code provides that the legitime of each illegitimate child is one-half of the legitime of a legitimate child, and that "except for this modification, all other provisions in the Civil Code governing successional rights shall remain in force." The Family Code also recognises a single class of illegitimate child, so the older Civil Code sub-classifications — natural, spurious and the rest — no longer sort heirs into different tiers. The one-half/one-half split between spouse and siblings survives; the antique labels do not.
Which brothers and sisters actually qualify
This is where families are most often surprised. The half-share does not go to everyone who calls themselves a sibling. The Civil Code draws a barrier between an illegitimate child and the legitimate relatives of his parents: they do not inherit from one another by intestate succession. So a legitimate half-brother of the deceased may be shut out entirely, while a fellow illegitimate child of the same parent is not. Nephews and nieces take only by representation, meaning in the place of their own parent who predeceased and who would themselves have qualified. Sorting out who is inside and who is outside this line usually decides the case before any arithmetic starts.
What to do next
Gather the documents that establish the two things the law turns on: the marriage of the deceased to the surviving spouse, and the filiation of everyone claiming as a sibling — birth certificates, records of acknowledgment, and the parents' own civil status records. Establish too whether either parent of the deceased was alive at the date of death, because that single fact can move the whole estate. Where the heirs agree, an estate can be settled out of court; where they do not, a judicial settlement is needed and estate tax deadlines run regardless. If the shares are contested, book a consultation before signing any deed of settlement or waiver.