Stopping elder abuse in the familly situation that you describe will be a complicated task. You may have to accept the difficult relationship between your brother and your mother.
mother will not tell agencies that there is any problem. She loves her son because he makes her happy and he helps her. She may fear that she will need institutional help if he is not there to help her. Or she may fear what will happen to him if she is not there to help him. One thing that is keeping your mother going is her love and concern for your brother.
A man depending on his mother, living on disability, talking drugs and biting the hand that feeds him is in terrible trouble. Your mother most likely feels guilty. His self esteem must be at the lowest ebb.
What can you do to intervene in their relationship? I would suggest that you move very slowly. At home I would suggest that you get counselling from a therapist who specializes in family dynamics. If you do not have funds for this, I suggest Alanon, a free service for the family of alcohoics or drug abusers. At all times work on yourself. Realize that you cannot fix the problems of your mother and brother.
In Georgia, you might get advice from the Adult Protective Services at 888-774-0152. You could consult an elder abuse attorney, the elder abuse hotline and the pastor at her church if she has one. Don't expect too much since your mother does not think that she needs help.
Most importantly, go to Georgia as often as you can. Try to have family reunions, family dinners and get togethers.Try to work on strengthening your love and connection in the most ordinary way. Try to remember happier times between you and your brother, before things started going so badly for him. Is there any way to love him apart from his neurotic behavior? Can you go for a walk, go for coffee, buy a smple shared gift for your mother. Try to work on developing patience.
And I wish you the very best. Stopping elder abuse is complicated. You have to go deep. It takes courage to let the pain of closest family connections open your heart. That is why I say go slow. Sometimes life is learning to accept what it is that you can't help.