Short answer. For the reserved portion (legitime), yes — Article 890 of the Civil Code says the legitime reserved for legitimate parents is divided equally between them when both survive the child. But this applies to the legitime specifically. How the rest of the estate is distributed depends on whether your sister left a will and who the other heirs are.
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 →
The equal split when both parents survive
Article 890 governs the legitime of legitimate parents: "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." This means when your sister dies without children and both parents are alive, each parent receives an equal share of whatever portion of the estate the law reserves for parents as compulsory heirs. If one parent had already died before your sister, the entire parents' legitime would go to the survivor.
What happens to the rest of the estate
The equal split under Article 890 addresses the legitime — the portion the law compulsorily reserves for the parents. Whether there is a free portion beyond that depends on what kind of heirs exist. If your sister died intestate (without a will) and had no children, the parents are typically the primary heirs and may inherit the entire estate. If your sister left a will, any free portion she could freely dispose of may have been allocated to specific persons or organizations. The parents' guaranteed minimum is the legitime; what they actually receive may be more, depending on the will and any other heirs.
When there are other ascendants instead of parents
Article 890 also addresses situations where neither parent survived but other ascendants (grandparents, great-grandparents) are alive. In that case: if the ascendants on both paternal and maternal lines are of the same degree, the legitime is split equally between the two lines. If the ascendants are of different degrees on each line, the closer degree takes everything from that line. This line-of-ascent analysis matters mainly when parents have predeceased the testator and grandparents or higher ancestors are still alive.
Practical steps in estate settlement
Even where the rule is clear — equal split between surviving parents — the actual estate settlement process involves identifying all assets, determining whether there are debts, and distributing the net estate according to the applicable rules. If your sister left a will, it must go through probate. If not, the heirs can execute an extrajudicial settlement if they are all of age, agree on the division, and there are no outstanding debts. A lawyer can help structure the settlement correctly to avoid later disputes over whether the parents' shares were correctly computed.