I wonder if he was trying to save face a bit in front of his brother when you had that interaction about the decking? It sounds like he likes having things on his own terms - the flat but also being able to come and go in the family home as he likes - total and unlimited contact with his children, but back-up wife work so he doesn't actually have to be a single parent. The conversation about the money and the decking sounded like him attempting to take some decisions and be man of the house, and I am not surprised he didn't like it when you pointed out that it wasn't actually his home any longer, and you'd be having full input into that decision yourself. I also think as he's the one who pretends to set boundaries (the business with the steaks) but actually just uses them to give punishments, he probably thinks that boundaries from you are about him - ie - punishments - rather than about your own comfort and security. So he'd expect a poor attitude from you, and when you continue being warm as well as having a boundary, he doesn't know what to do with himself. I've noticed similar behaviour from my H in the past, but I can just never quite sustain it.
