I am curious. You don't mention talking to the brother directly. Does the brother know about this? Has there been any discussion with him and what might want from such a relationship? (Assuming he is willing, of course.)
I ask because you and your husband could figure out all the ins and outs for yourselves and be flummoxed when he wants input. Or he may not be interested. The work you're doing isn't wasted at all but I can just envision a scenario where you and your husband present this to him, all angles covered in your discussions, and he isn't into it or brings up something y'all hadn't considered. Happens all the time. Talk among yourselves, absolutely, but leave room for him to make a place for himself in the potential V here.
And this would be the same advice I would give to any one considering a V or triad.