Is it permissible for a mother to donate her share of her deceased son's inheritance to her son's children, while she has other heirs?

It is permissible for a grandmother to gift to her son's children what she inherited from him, by transferring ownership to them immediately. It is preferable to be equitable between grandchildren and children, unless there is a legitimate reason for differentiation. Ibn Hajar al-Haytami said: "It is sunnah (definition) for a parent to be equitable in giving gifts to their offspring, no matter how distant, even grandchildren alongside children. If they are not equitable without an excuse, it is disliked by most and forbidden by a group." The gift should not be made conditional upon her death, as that would make it a will. A will is not permissible for more than one-third of the estate unless the heirs permit it, and grandchildren do not inherit if there are surviving sons.