My parents know there's no way of controlling me anymore. But they won't let it go. If they cared about me and what they did, they'd apologize. But it's never happened.
I genuinely like that you're still optimistic, but I really wish you'd set re-think/reset this whole mindset.
You're parents are both mentally ill.
They
don't know they can't control you. If they did, they would act differently - for example, your mother's email (from a few months ago) would have been significantly different. They believe they care, and that they're acting in the best possible way.
So it's not "
reluctant to let go" on their side, it's "
how can we help deluded Autotune understand the real situation".
This is the (most likely by far) reason they haven't considered apologizing, despite it being the obviously best action on their part. They're don't see it as an option, because they
"know" they're done no wrong.
Which brings us to the point of this post:
Your wanting them to apologize is "symptom" of the reason it's hard for you to handle them.
It significantly weakens your position.
As a secondary goal it requires that you always keep the possibility of negotiation open. Which limits the options open to you, literally starting with the initial contact.
You need to take an absolutely neutral position, focused only on the primary objective..
Wanting a "fairytale ending"
weakens you, Ditto a wish for "payback".
You (your "side") should do exactly what's needed, neither more nor less, until the primary objective is definitely achieved.
This isn't easy of course, especially for a naturally agreeable person. But that can be handled by your avoiding direct contact, hence the need for an intermediary.