Hi and welcome to SR, Overwhelmed1.
My experience with couples counselling, is that it takes time and lots of it, when communication isn't good in the first place. when they are in denial, its even harder. Your therapist would need good training in addiction counselling, I would think, in order to have a good grasp on what is actually going on with your hubby.
About your brother, I cannot say, but has he been to a doctor and discussed his situation? Its pretty much up to him, and if your Mother enables, he may not do much.. we just can't make them do anything. I would imagine your mom knows how ill he really is.
focus on yourself, would be my advice. find out what you want out of life. I hope the counselling helps. Will he go to AA, also? He is probably going to need more than just marriage counselling.
good luck to you and keep posting. I hope someone else with experience with an A spouse will come along and share with you.
take care!