Poor you. It's just like being pulled every which way. All I can say is that you must try to keep things separated. You don't have to facilitate contact, but I think you may need to allow it for now. But let him do all the logistics and present you with a proposal which either is or is not convenient for YOU.
The cheque thing was very childish of him. But don't let him get to you or try to make you do something not in your best interest. You know that's what they're trying to do.
Things are off kilter here. My brother has fallen off the wagon, hard. He's in rehab now. Breaks my heart, he really hates himself when he falls. Just say a prayer or think a good thought for him. He's a lovely man and so devoted to our mother.