My brother does not pray, curses religion, and commits grave sins. Should I advise him or leave him be? And how should I deal with him as a sister?

Undoubtedly, your brother is in grave danger. Cursing religion is disbelief, and abandoning prayer is one of the greatest destructive sins. It is obligatory to advise him and call him to Allah by every possible means. If he does not respond, then if boycotting him is more beneficial for him, boycott him. But if maintaining ties with him is more beneficial, then maintain ties with him to the extent that the objective is achieved.