Is it permissible for a husband to relinquish his share of inheritance and his apartment provided by his work to alleviate his feelings of guilt for receiving more financial support from his father than his brother?

The preponderant view, in our opinion, is that equality among children in gifts and donations is obligatory. As for expenses, equality among children is not obligatory; rather, the father spends on his children according to each one's needs. What your husband's father gave to his son, whether money, apartments, or other things, in excess of the usual maintenance, he is obligated to equalize it between him and his other children. Equalization can be achieved in one of two ways: either by giving his other children the same as he gave the first, or by taking back what he gave to the first, if possible. Therefore, the correct course of action is for your husband to endeavor to return what his father favored him with, so that he may be equalized with his brother in the gift.