Hi Bigsis,
Sounds very similar to my brother's story except that he's still hanging in there. First, you need to tell your brother to buck up and tell him there are consequences for his decisions. He is choosing to stay in the bed that his wife made. I know I don't sound very sympathetic, but I have to tell you that my brother would moan and groan and then not take any action. He wanted to have his cake and eat it too, that is, he wanted sympathy, wanted us to feel like
we had to do something, while he went off to work and left us with the mess. Like, here, fix this for me while I go focus on making money. Take her off my hands so I can look helpless and nice. Then if
we had a complaint about her, he was spineless enough to act "dumb" like he didn't know what we were talking about.

I ran out of sympathy.
I don't know if my brother is seeking counseling now that we have stop buying into his act, but I am glad that your brother is. It will help tremendously. And tell him to stop putting bullets in his wife's gun (like informing her that he is seeking counseling.) That said, go to
www.bpdcentral.com and look up their book about divorcing the borderline spouse. His wife does sound destructive.
I believe that stepping aside has actually improved my brother's situation (maybe not in his mind) by causing him to take responsibility for his own decisions vs. staying stuck in the victim stance.
I apologize for sounding impatient. It is the impatience with my own brother that you are hearing. I also encourage you to limit your own involvement in all this. I advise that you can be loving, caring and supportive. "suggest and leave" as you would with a teenager. And don't be surprised if the response is "Yes, but". If he is in the army, he may be used to other people giving the orders. But this is his life.
Good luck to you and your brother. Seeker