Is it permissible to sever ties of kinship with a brother who quarrels with his mother, disrespects her, and uses immoral language, especially since the mother is displeased with him and will not forgive him?

Disrespecting parents is one of the gravest major sins. However, a brother's disrespect towards his parents does not negate the obligation to maintain ties with him, as the Prophet, peace and blessings be upon him, said: "Yes, maintain ties with your mother." But you must advise your brother, explain the danger of his actions, warn him about the consequences of disrespecting parents, give him useful books or tapes, and supplicate for his guidance. If he does not heed the advice and shunning him would deter him, then boycotting him becomes obligatory. You should also seek forgiveness from your mother and ask her to supplicate for his guidance, as a parent's supplication for their child is answered.