Is the second floor considered the property of the youngest son based on his claim that his father gifted it to him, given the absence of witnesses and the testimony of the deceased mother, and what are the implications of some heirs signing while others refuse, and what is the Islamic legal ruling for someone who tries to seize a right by force?

A gift is not completed unless possession is taken during the donor's lifetime, while they are of sound health and legally competent to dispose of property. If possession is not taken, the gift is not established and is considered part of the heirs' estate. Therefore, if a father gifted something to one of his children, and the child did not take possession of it during the father's lifetime, that item becomes part of the inheritance. Consequently, if the mature and discerning adult siblings consent to this gift, it is affirmed for the recipient. However, if they do not consent, they have the right to demand their share or compensation for it. The son must fear Allah and return rights to their rightful owners.