Is it permissible to count what is spent on the fiancée and her sister from zakat money before marriage, and does the fiancée's purchase of a gift for the son from this money affect the reward of the zakat? Is it obligatory to accept the return of the amount if the two eligible recipients no longer need it, and do the son or father sin by helping the fiancée's sister seek divorce from her ill-tempered husband?

It is permissible to give zakat to the girl and her sister if they are poor and their livelihoods are insufficient. There is no blame on the son for giving his zakat to the girl if she is not someone whose maintenance is obligatory upon him. The intention behind giving zakat must be to seek closeness to Allah. What was spent on her previously without the intention of zakat is not counted as such, and zakat is not valid except with intention. If the girl and her sister receive zakat and are entitled to it, they own it and can dispose of it as they wish. It is not necessary to inform her that what is given is zakat, unless it is known that she will not accept it if she knows its true nature. If the girl becomes self-sufficient, it is not permissible to give her zakat after she has become self-sufficient. If the sister's husband's فسق (immorality/open sinfulness) is proven, such as his drinking alcohol, drug use, illicit relationships, or his refusal to provide maintenance without a legitimate Sharia-compliant reason, or his mistreatment of her, then she is permitted to seek a divorce, and it is permissible to assist her in that.