What is the ruling on giving the remaining apartment to the youngest son with the consent of his siblings after the father's death, and what is the ruling on the father writing his apartment to the eldest son, who married and then moved out of it, while there are other children for whom the father cannot provide apartments?

The inherited apartment is the property of all heirs, each according to their rightful share. An adult of sound mind may waive their share to one of the heirs, and there is no objection if all adult heirs of sound mind waive their share to one of them. As for a minor or someone of unsound mind, their waiver is not considered valid, and their share remains preserved for them. It is not permissible for a father to grant a gift to some children to the exclusion of others, nor is it permissible for him to make a will stipulating that the apartment goes to one of the heirs after his death, as a bequest to an heir is forbidden by Islamic law.