Short answer. All the heirs are liable, in proportion to their respective inheritance. Article 926 provides that when the testator does not charge any particular heir with a legacy, every heir is bound to contribute toward it in the same proportion in which each inherits from the estate.
What the law says
When the testator charges one of the heirs with a legacy or devise, he alone shall be bound.
Civil Code, Article 926 — Charging One Particular Heir. Read the full provision →
What the law says
Should he not charge anyone in particular, all shall be liable in the same proportion in which they may inherit.
Civil Code, Article 926 — Charging One Particular Heir. Read the full provision →
The default rule when the will names no particular heir
Article 926 answers your exact question. It provides that "should he not charge anyone in particular, all shall be liable in the same proportion in which they may inherit." Because your will did not single out a specific heir to shoulder the legacy, responsibility for satisfying it falls on all the heirs together, rather than on any one of them alone.
How the proportion is determined
The article ties liability directly to inheritance share: each heir contributes "in the same proportion in which they may inherit." An heir who receives a larger share of the estate bears a correspondingly larger share of the burden of paying the legacy, while an heir receiving a smaller portion contributes proportionally less. This keeps the financial weight of the legacy aligned with how much each heir actually benefits from the estate.
The contrast that explains why this default exists
The same article shows what happens when the testator does make a specific designation: "when the testator charges one of the heirs with a legacy or devise, he alone shall be bound." That is the exception — a testator can single out one heir to carry the whole burden. Where the will is silent on this point, as in your case, the law does not leave the question unanswered; it falls back on proportional liability among all the heirs rather than leaving the legatee without a clear source of payment.
What this means for the heirs and the legatee
For the legatee, this rule means the legacy is backed by the collective estate rather than resting entirely on one person's willingness or ability to pay. For the heirs, it means each of them should expect to contribute toward the legacy according to their respective inheritance shares, rather than assuming the obligation belongs to someone else simply because the will did not name a specific payer. Sorting out exactly how much each heir owes toward the legacy requires knowing each heir's proportional share of the overall estate, which is usually already established during the settlement and partition of that same estate.