1. If the gifted land was the self acquired or separate property of your grandmother she was at liberty to gift, sell or bequeath or mortgage it during her lifetime. The right of a title holder to deal with his property in the manner desired by her is unquestionable.
2. The donees i.e daughters of your grandmother have the remedy of filing a suit for recovery of possession against your father as the possession given to your father was only permissive in nature.
3. Your father can claim a share in the land he has been cultivating if he can prove that it was ancestral property which could not have been gifted by his mother.