DH says that he badly wants to be able to operate in our house as though we don't depend on BM for anything. She will never ever pay what she owes, she will never ever do the right thing, she will continue to just suck until we all die. We get this.

However...the terrorist negotiations just can't seem to end. This weekend's angst was all about soccer tryouts: if she will take the twins to tryouts on her custody time, because she thinks that their social calendar is more important. They want to attend tryouts and miss a couple of the fabulous (fifth grade) social functions that she has arranged for them to attend. DH finally was able to convince her how important it is to attend tryouts of something that you are hoping to be chosen for and now the problem is that the musical instruments that we rent for them (for which she has been erratic in her payments and has now stopped paying her share of) she wants back at her house so that they can practice over the next couple weekends they are with her. I thought we had a plan- that as she is not paying for any part of them, they will stay here in this house. DH said this in an email to her yesterday, and he told the twins yesterday that they would need to leave them here. So guess where the instruments got dropped off this morning? Her house. Because he is afraid of pissing the terrorist off, and that thinks that if she becomes mad about his refusal to allow the instruments (that she pays no part of) come to her house, she will not bring the twins to tryouts. Irony is that she will not and has not for the past several years paid for a cent of their soccer either.
Twins don't know consistency from either parent: her because she's a fucking lunatic and DH because for the most part he feels like he has to negotiate with her insanity and spite so that the twins aren't penalized by stuff they have no control over. Twins are 11.

CAN this end soon? Anything out of their mouths she immediately thinks is DH's- like if they tell her they want to attend soccer tryouts she'll say their father has been brainwashing them.

And of course it's my name on the instrument rental. If she "loses" the instruments, which she would absolutely do or lie about, it's to the tune of at least a couple thousand dollars, I'd think. Am I nuts to be worrying about this? Is DH doing the right thing by playing these games? Is there a way to stop the insanity?