Do the mother and the rest of the children bear a sin for not speaking to the son, in rejection of what he did to their father and in obedience to the father's wish?

A brother's behavior towards his father is among the gravest forms of disobedience (ʿuquq) and one of the major sins. He should be advised and warned about the consequences of disobedience. If he does not heed the advice, then boycotting him is permissible; in fact, it may become obligatory to rectify him or to avert his harm from you, while prioritizing maintaining ties with him and continuously advising him if there is hope for his reform.

However, if the brother repents, then boycotting him is not permissible, because repentance erases what came before it. In such a case, obedience to the father's command to boycott him is not obligatory, as obedience is only in what is good and lawful (maʿruf).