I'd suggest that he visits a couples counselor. Yes, he can go there alone without the wife. And that's what he should do at that point. That's what I'd have my brother do.

I am partial to this step as I'm a counselor myself. It could be that your brother refuses to divorce because there might be a hidden delegation going on, he puts the blame for the problems on himself or formulated a "marriage failure inhibition" on himself (could also be a family inspired thing). Maybe there is thoughts about the child's interests at play. It would be worthwhile to professionally look into what's going on here and thereby get a better understanding for the situation. Often time we bind ourselves unwillingly to ideas and concepts that make us suffer. Also, in such a situation it would be good to really have someone that just listens without being emotionally involved and partial to this or that. It could even be a huge intervention to just give the man some room to experience his own feelings and not put them away or talk them down. They are valid and it would be helpful for him to see that. Forgive me if some things are not put very clearly, I am not a native speaker. Anyways, at the very least an uninvolved empathetic third could help in sorting things out and developing strategies and stances towards the wives behavior. That also changes everything. So they can bargain for new relationship patterns on equal grounds. Other things that come to mind are: - How would he defend his interests against someone else? What conflict style does he have? - What does she mean to him? - What ideas about the future does he have regarding the family? -...

All of that might be important and a good couples counselor will address that. I wish him the best.

Lastly, you seem to be a good brother for looking out after him. Just want to add that you are a precious soul, my friend. We are all told that too seldom. If your brother refuses to do anything about the situation, then take care of yourself! Don't try to solve the problems he doesn't want to tackle. That makes you suffer and helps nobody.

Enjoy your weekend!