Thumbs up and hats off to you, RJD!
You deserve credit for a lot. You not only did what you could for people who sound like they have no concept of "gratitude." At the very least, take credit for not strangling both of those whining slobs before that plane had landed!
I agree, that you've allowed them to waste your time and efforts, and then to come up with more demands on you. You are going to have to close that door. We put up with children because we have hopes that they will grow up and take care of themselves one day. But these folks don't seem to have any intention of doing that!
Your fury is not going to help until you channel it into cutting them off. Otherwise you turn it inward, as you know. You certainly deserve to tell them something like: "Hey, listen up! I've got problems of my own to handle. You are legally adults. Act like it, and stop expecting me to clean up after you ever again, because I will not."
Of course you will have to back it up. I guarantee they will try again!
I also understand from experience the fury you feel toward your mother for her abuse. There is a wrongfullness in a mother violating her bond of trust that can hardly be described. Even if there was no physical violence. Even if her abuse was covert, perhaps hidden under her "caretaking responsibilities" so that it did not LOOK like sexual abuse.
That was the case with me, but it was still was a powerful factor in my psycho-sexual development, and I held furious for years about it. I would like to disclose my own story here, but perhaps in another letter.
Good luck and stay strong!