Is it permissible to use a general power of attorney to sell the father's share of his father's house to his son, with the intention of returning the rights to the brothers and mother later?

General agency is a matter of scholarly disagreement. Some scholars prohibit it due to the presence of gharar (excessive uncertainty), while others validate it. Special agency, however, is valid without dispute. The Hanafis and Malikis validate general agency, whereas the Shafi'is and Hanbalis do not validate it due to the significant gharar it entails. The agent acts within the limits of what the principal has authorized him to do, and it is not permissible for him to exceed that. It is also not permissible for an agent in a sale to sell to himself without the permission of his principal.