There's honest opinion, emotional illiteracy and not being able to see the wood for thw trees.
To those putting the boot in:
How many times do we see a woman come on here and ask 'AIBU to ask H to pick his clothes up off the floor before I kill him?
People pile in, saying killing him is AIBU, yeah he could pick up his own stuff, but your're a SAHM, wouldn't kill you to do it now would it?
Then it turns out there's more than meets the eye.
This situation is similar. These are not usual circumstances, and it would appear that OP is being treated differently to her brothers, and is on the end of some vile and crappy behaviour. On top of this, she's got a challenging parenting situation.
We could all forgive her DF not letting her off with deferring a payment, but it does sound somewhat reasonable for OP to ask, and certianly doesn't ever warrant a comment like the one he made.
The question was 'AIBU, or are my parents a complete waste of time'
To all intents and purposes, for all manner of reasons, to the OP it would appear that She INBU in some ways, and her parents have and ARE not being as supportive as most other parents are.
Sometimes the story is bigger than the original opening post. I'd hope that anyone spending more than a few hours minutes of their life on Mumsnet has learnt that there's more than meets the eye sometimes, to look closer, and consider people's feelings by not judging/insulting someone clearly in some turmoil.
My advice OP, deep breath, let yourself stop for a moment and try to see a rational alternative to your family. No-one can think when they're worked up.
What you called Couple Time is called Respite in your situation. You need a break. As other posters have suggested, could your DP parents help out?
Come over to Relationships or SN boards. Stately Homes might help a little too.