What is the ruling on, and is it permissible to carry out the husband's verbal will to transfer ownership of real estate to his daughter after the wife's death, with the son's consent and waiver, and how is this waiver documented?

This is a bequest to an heir, and a bequest to an heir is not valid unless the other heirs approve it, due to the Prophet's (PBUH) saying: "Indeed, Allah has given every rightful person their right, so there is no bequest to an heir, unless the heirs wish it." So, if the heirs agree to execute the bequest and relinquish their right to the apartment in favor of the daughter, there is no objection to that. As for how to implement this legally, legal experts should be consulted.