Again, your thread is chock full of so much wisdom and advice, it is really interesting and valuable to read.
I totally get the reasons why a S doesn't work for you right now. I personally believe it might be the easier path to M 2.0, but I understand that it is not the better choice for you as a family at the moment. It may be the more difficult path, but you strike me as a person who is not afraid of hard work, so I completely trust in your ability to navigate this. My point of view is preempted on you healing this M while living under the same roof.
To expand on some of the earlier advice, what would it look like if you made a spreadsheet of 'issues I have control over (ie me), issues I don't (ie H) and where we meet (the M)'. Compartmentalizing has been a huge help in detachment for me. It is a daily reminder of what I can control and what I can't. You have a lot of blurry lines right now, and I think if you were really honest with yourself (through a list like this), you will find those arenas where you are able to detach. I won't go into a list of what I see in your posts, other posters have pointed them out, but it might be a helpful exercise.
Something happened recently in my situation where I was confronted with an interaction with H that I was able to do a complete 180. (Thanks to detachment). I was a fly on the wall observing the interaction between us, while still being a participant in the interaction. I will go into more detail on my own thread, but the end result was an awareness of how my previous responses, though intended as being helpful, loving and supportive, were actually truncating H's ability to feel the whole spectrum of his own emotions (most of them bad) and therefore not allowing him to acknowledge, learn and heal himself.
Allowing a person to experience the full gamut of their emotions, their experience and their narrative, with little influence from yours is really the swiftest path to healing. And regardless of how much H has f*cked up, he still deserves to have his own feelings, his own process in all of this, separate from you and yours.
You are telling H how he should feel right now. Whether covertly (silently upset, angry), or overtly ('May won't be invested in M 2.0 until he feels differently about AP'). So his feelings are dominated by you. Which to his credit, amputates his ability to feel all the emotions within himself, learn from them and move on to the place he really wants to be (which I truly believe for him is M 2.0). You are unhappy with an inauthentic response from him, but at the same time you are setting him up for failure because deep down, his authentic response is antithesis to your needs. His authentic responses, feelings, growth are superseded by his desire to keep you happy, to keep you present and working on M 2.0.
This is why S work in these scenarios. But in the absence of a S, you are going to have to do the doubly-hard job of separated YOUR feelings from your desires of H's feelings that trend in your favor.
Which brings us back to the list. What can you control? What can't you control?