What is the ruling on differentiating between children in gifts, endowments, and marriage expenses, and how are these rights restored, and is it permissible for the son's wife to demand from her husband's mother the like of what she gave to her other son?

The father, and the mother as well, must be just among their children in giving gifts, whether small or large. It is not permissible to favor one over the other except for a legitimate Shar'i reason. So, whoever favors one of his children must return what he gave or give the others a similar amount to achieve justice. The son's wife has no right to intervene in demanding her husband's share, for the right belongs to the son alone.