What is the ruling of the religion if the grandmother's children cut off ties of kinship with the questioner, after they learned that she had written a portion of her inheritance to him, not exceeding one third, knowing that he is not an heir?

Severing ties of kinship is forbidden and is considered one of the major sins. To whoever has had their ties of kinship severed, we advise them with the counsel of the Prophet, peace and blessings be upon him: "Connect with whoever severs ties with you, give to whoever deprives you, and forgive whoever wrongs you." As for the grandmother's bequest of a portion of her wealth after her death, as long as it does not exceed one third, it is a valid will that her heirs are obligated to execute, provided it is for someone who is not an heir and remains within the limit of one third.