What is the ruling of Islamic law regarding my paternal uncle's wife's usurpation of my mother's land through forgery, and what sin results from this for the deceased and for my mother, and what must my mother do to restore her right?

If the mother verbally confirmed her waiver of her share to her brother, and then the maternal uncle's wife completed the official procedures in the mother's name, and the mother ratified this waiver during the maternal uncle's lifetime and did not reject it, then the children have no right to the land. This is because it passed out of the mother's ownership through a gift and possession, and it is not permissible to revoke it, for the Prophet, peace and blessings be upon him, said: "The one who revokes his gift is like a dog that returns to its vomit." The misconduct of the maternal uncle's wife by impersonating the mother does not invalidate the gift.

However, if the mother changed her mind before the transaction was completed and did not acknowledge the maternal uncle's ownership of the land, and was not pleased with his wife's action in her name, and the maternal uncle knew about this but did not return the right, then they are usurpers of the land. The heirs must clear their deceased's conscience by returning the right, for the Prophet, peace and blessings be upon him, said: "Whoever usurps a hand span of land unjustly, Allah will encircle him with it on the Day of Resurrection from seven earths." The mother incurs no sin if she remains silent, and she has the right to demand her right or forgo it.