Are the deceased daughter's children entitled to claim her share of the gift that their grandfather gave to his son (their maternal uncle) twenty years before her death?

It is permissible for a person to donate all or part of his wealth to his children during his lifetime, and there is no original objection to that. Al-Mardawi stated in "Al-Insaf" that it is not disliked for a living person to divide his wealth among his children, according to the sound opinion of the madhhab (definition). The donor must equalize among his children in the gift, as Ibn Qudamah narrated from Imam Ahmad. For this gift to be valid, specific conditions must be met; if they are met, the questioner may demand his mother's share of those lands.