Yay - the house is (sort of) yours . That is definitely cause to celebrate. Your MIL sounds like a rock star. Not that it matters, but your H sounds like he is isolating himself. What a fool.
'Transition' to me means a softer version of MLC ... if so, keep away. Let them go through that [censored] on their own time. Tell him to come back when he has finished transitioning and is now 'transitioned'.