Can you get him to sign on to sober recovery?? Perhaps then he could see he is not alone.
He seems to still be in love with your Mom. He needs to understand that if he does love her, he must cut her off and let her hit bottom. He must also look after her children, if he truly loves her. (Thats what she would want if she were of sound mind and body.)
He needs to get divorced and cut all financial, tax, and social ties with your mom to protect his and your interests.
He is not helping your Mom, he is hurting her. Tell him that and try to get him to log in here ar SR.