Is it obligatory to boycott a brother who is undutiful to his parents and mistreats his siblings?

Disobeying one's parents is one of the gravest sins. The questioner should offer advice to his disobedient brother, warning him about the danger of disobedience and cutting off kinship ties. He should respond to evil with good and seek help from those who can influence his brother to advise him, along with making supplications for him. If his brother does not desist, then it is permissible to boycott him if the boycott serves as a deterrent.