Is the division that took place verbally between the father and his children, in which the father allocated the first floor to two of his sons, and half the area of the second floor to his married son and his sister, Islamically valid, given that the married son rejected it and wants to change it, and must it be redone?

The land and the house are the property of the father, unless there is an agreement between the father and the son who participated in the construction that what he built is exclusively his, to the exclusion of his siblings, or if custom and tradition dictate that. If there is no agreement or custom, then the land and the house are the property of the father. He must be fair and equitable in the division among his children, based on the hadith: "Fear Allah and be just among your children." It is permissible to favor some children for a valid need or a realized benefit, and favoring one who strived, worked, and spent money with his father is permissible according to Islamic law.