Your GF (his ex) has no other home and no money other than his payments to her. So how "free" is she to tell you how she really
feels about you, about him, or about the dynamic?
When one wrong word could mean you guys kicking her out of the home, stopping payments, and her having to chase him through the courts for it? All with having to provide for the kids and start all over?
That's what I mean about a skewed power dynamic.
She may SAY pretty things to you and to him... but how authentic could it be?
You keep "fighting" to make a thing that won't naturally fly, fly.
Your hubby seems like he is in it for ulterior motives -- "to set her up" an gain legal custody of the kids.
That's all messed up sounding to me and does not bode well. It does not sound healthy to me. I am sorry.