Oh, none of that was clear from your introduction, mostly because you wrote in that: "I want to know if he's broached this subject with his wife... and how does she feel about having a third person in their life?" So, by that you meant really just changing living arrangements? Sorry I was confused!
So, you are already involved as lovers, romantically, and have been for a few years now. And you know for certain that his wife is aware of this relationship he has with you and she consents to it. Correct?
Does she have a friendship with you as well? Do you ever socialize with her? Or is it kind of like she knows about you but there's no relationship between you?
Now he wants to either have a separate home with you or have you all move in together. You, of course, want to know how your metamour feels about that. To me, it would seem nigh on impossible, and untenable, to share a household among all three of you if you don't have some sort of relationship with her or at least know how she feels about it. Otherwise, it would feel like a weird roommate situation. There are several members who live together in similar arrangements, so they would have good real-life experiences to share with you about that (not me - I live alone and prefer to stay that way, LOL).
So, now that I have more information, I can see why it might be better to live separately from them -- but all three of you living together could work very well. Either way, all the things you wonder about need to be asked.
So, what is it that prevents you from asking to speak with her? In your intro you wrote: "How does he envision it working if I moved in, or if we had our separate home. How does he plan to share himself with both of us?" These are all questions you need to ask him.
I guess what I'm wondering is why the hesitation or trepidation about asking this man all the questions you pose in your posts here? Is there something I'm missing?