Is the son's acceptance of his mother's offer to sell him a portion of her land in exchange for him performing Umrah on her behalf, with the father's approval, considered an injustice to the rest of his siblings?

Parents must treat their children equally, male and female, in gifts and endowments. It is not permissible to favor some over others except for an urgent need or with the consent of all. Justifying the preference for males due to their need for housing is not valid, as this need can be met through lending or renting. It is also not permissible for a mother to show favoritism to any of her children when selling her share of land, as favoritism in selling is akin to a gift. If not all siblings agree to the favoritism, then accepting the preferential gift is not permissible.