the subject is strongly claiming the allegation of mental illness is defamatory and there are ongoing complaints about it at WP:OTRS - I support keeping it out - it seems the subject is estranged from his brother and that is the only source of the information. I would like to see some reliable independent reports of the claims before I would feel ok to add it. Leaving out what is a complained about single  claim of mental illness without additional sourcing is at this time the better option in the BLP at this time. Regards.I see you are a very new editor and a WP:SPA in regard to this controversial BLP article. -