Is it permissible to boycott aunts who commit adultery for money, as well as aunts who do not commit it but support those who do?

Adultery and assisting in it are among the major sins. You must advise your female relatives to stay away from what Allah has forbidden and encourage them to obey Him, and warn them against disobeying Him, for "religion is sincerity (or sincere advice)." Forsaking a disobedient person is permissible if it deters them from the vile act; otherwise, you should maintain ties with them and continue to advise them.