How should I deal with my brother who is disobedient to our mother, knowing that he does not accept advice, and may Allah be pleased with my actions?

Disobeying one's parents is one of the gravest sins (major kabirah sins), and Allah and His Messenger have forbidden it. Whoever commits it will not enter Paradise. The questioner must maintain ties with her disobedient brother and remind him of the sin he is committing, and she should pray for his guidance. It is permissible to temporarily cease interaction with him if that will bring him back to righteousness, provided all other methods have been exhausted.