Is the gift made by the grandfather limited to money, or does it include his legitimate share of the lands and houses left by the father, and is the testimony of the grandfather's wife in this regard sufficient?

If it is proven that your grandfather gifted you the money he paid to your uncle, then this is a specific gift pertaining to that money, and not to his entire share of the inheritance, unless it is proven that he also gifted you the remainder. The testimony of the grandfather's wife alone is not sufficient to prove the gift.