Short answer. Yes. Article 890 divides the reserved portion between father and mother equally, and where one of them has already died the whole of it passes to the survivor. It does not split with anyone else, and as siblings you take nothing from that reserved part.
What the law says
The legitime reserved for the legitimate parents shall be divided between them equally; if one of the parents should have died, the whole shall pass to the survivor.
Civil Code, Article 890 — Legitime Of Legitimate Parents. Read the full provision →
What the law says
In default of legitimate children and descendants of the deceased, his parents and ascendants shall inherit from him, to the exclusion of collateral relatives.
Civil Code, Article 985 — Parents and Ascendants Inherit Next. Read the full provision →
The survivor absorbs the whole reserved share
Article 890 answers the question in one clause: the legitime reserved for the legitimate parents shall be divided between them equally; if one of the parents should have died, the whole shall pass to the survivor. Your mother does not take a half and leave the other half unclaimed, and the predeceased father's half is not passed down to his own relatives. The reserved portion is a single share belonging to the parental rank, and the living parent takes all of it. The same logic applies when a grandparent stands in a deceased parent's place.
But 'the whole legitime' is only half the estate
The phrase does a lot of quiet work, and it is worth being precise about what it covers. Where a person dies without children or descendants, the legitime of the parents is one-half of the estate. Your mother takes the whole of that half. The remaining half is the free portion, which your brother could dispose of by will as he chose. So a mother inheriting 'everything' is not what the article says; she inherits the reserved half as of right, and whatever else the will or the rules of intestacy give her.
Where a widow or an illegitimate child changes the arithmetic
Both draw from the free half, not from the parents' share. If your brother left a wife but no descendants, she is entitled to one-fourth of the estate, taken from the free portion. Any illegitimate child of his also has a legitime charged against that portion. None of this reduces your mother's half — it reduces what is left over. The order of satisfaction matters when the estate is small, because the free portion can be entirely consumed before any voluntary bequest is reached.
Where the siblings stand
Brothers and sisters are collateral relatives and are not compulsory heirs, so nothing is reserved for you. Article 985 puts it beyond doubt for intestacy: in default of legitimate children and descendants of the deceased, his parents and ascendants shall inherit from him, to the exclusion of collateral relatives. You can still take under a will out of the free portion, and you may inherit from your mother in time. What you cannot do is claim a share against her in your brother's estate.
Related provisions
- Civil Code, Article 890 — Legitime Of Legitimate Parents
- Civil Code, Article 889 — Legitime of Legitimate Parents
- Civil Code, Article 985 — Parents and Ascendants Inherit Next