Short answer. No. When a will is unclear, your father's intention is drawn from the words of the will read against the circumstances in which it was made, but the law expressly excludes his oral declarations of intention. What he said aloud about what he meant cannot be used to interpret the ambiguous provision.
What the law says
the testator's intention is to be ascertained from the words of the will, taking into consideration the circumstances under which it was made, excluding such oral declarations
Civil Code, Article 789 — Curing Ambiguities. Read the full provision →
Spoken wishes are shut out
Article 789 is explicit about the sources allowed when a provision is uncertain: the testator's intention is to be ascertained from the words of the will, taking into consideration the circumstances under which it was made, excluding such oral declarations. So even a truthful account of "what Papa always said he wanted" cannot be used to fill or bend an ambiguous clause. The will speaks through its written terms; testimony that the testator privately meant something the words do not carry is precisely the kind of evidence the article keeps out.
Why the law refuses them
The exclusion protects the will from being overwritten after the testator is gone. He cannot be called to confirm or deny what he supposedly said, so oral accounts of his intention are both unverifiable and dangerously easy to invent, especially by those who stand to gain. Wills are held to strict form for the same reason. If a relative's recollection could redirect a gift, the safeguards of a written, witnessed instrument would count for little. So the law fixes intention to what the testator committed to writing, not to what anyone reports he later said.
What the court may consider instead
Excluding spoken wishes does not leave an ambiguous will unreadable. The court works from the words themselves, read as a whole, and from the circumstances under which the will was made, the state of the testator's family and property, his relationships, the situation existing when he signed. Extrinsic facts of that kind are admissible to clear up an uncertainty; what is barred is the specific category of the testator's own declarations of intent. The aim is to understand the words he chose in their real-world setting, not to substitute a different intention for them.
The line that decides admissibility
The distinction to hold onto is between surrounding facts and reported intent. Evidence that your father owned only one parcel matching a vague description, or that a named legatee was the only relative of that name, is about the circumstances and can be received. Evidence that "he told me the house was really meant for me" is a declaration of intention and cannot. When the will is offered for probate, build your case on the documentary and factual context, because that is the material the court is permitted to weigh.