Is it permissible for a mother to grant a house to one of her children, knowing that the father had granted it to the mother for her usufruct as long as she is alive, and that it should revert to the heirs after her death, and there is a written document to that effect?

A gift (hiba) is not executed except through possession (hiyaza) or seizure (qabd). It is not valid to possess or seize a house in which a married couple resides if the husband gifts it to his wife while he continues to live in it, because his residence in it is for the man, and it is not valid for the wife to possess the house while the husband remains in it.

Similarly, the gift is not permissible if the property of the donor remains in the house, as the occupation of the gifted item by the property of the donor prevents the completion of the gift.

If the possession is not completed before the donor dies, the gift remains the property of the donor and transfers to his heirs.

If the gift is valid and executed during the father's lifetime, and the house transferred to the mother, then it is not permissible to favor some children with a gift without a legitimate reason.