How do I prove a will made for my great-grandfather?

A will is validated either by the heirs' affirmation of its authenticity or by evidence. If it is merely a statement or a writing in the testator's own hand, without witnesses or his saying "execute it," then it is not enforced, and the inheritance is divided among the heirs, unless the heirs affirm it and agree to its execution. If some heirs affirm it but others do not, and there there is no evidence, it is enforced only against those who affirmed it, according to their share.