Is it permissible for a father to distribute his possessions among his children, favoring the poor among them, and is it permissible for a rich brother to relinquish his share to his poor sister?

A father must be just among his children, male and female, in giving gifts. It is not permissible to prefer some over others except for a legitimate Sharia reason, based on the Prophet’s (peace be upon him) saying: "Fear Allah and be just among your children." Many jurists have affirmed the obligation of justice, and some have stated that an unjust gift must be returned, even after death. If the father is just in giving gifts and the children take possession of the gift during his lifetime, it is considered a valid and enforceable gift, and an adult of sound mind may waive his share.