I (22F) moved away from my parents (60M, 59F) a few years ago. My sister (20F) still lives there, and they drive each other crazy. What do I do?

I grew up in Maine with my parents and little sister. We're a well-off family, never really wanted for anything, but my parents were often very upset with us, growing up. My sister and I both got bad grades (to them, at least--we were C students), hung out with people that our parents didn't particuarly like, snuck out, talked back, etc. All standard teenage shit. Thus, I thought my parents' angry reactions were completely normal, and I just fought my way through my teenage years before finally moving to Florida for college.

Immediately upon moving significantly far away, things began to improve for me. My grades in college were wonderful, I was able to make and keep friends, I came out and finally was able to indulge in some semblance of a sexuality. But--most importantly--I went to therapy for the first time, and found that I wasn't just your rebellious teen with tsk-tsking parents.

My parents are on an emotional hair trigger. The littlest things can set them off. Looking back on my teenage years still sort of fills me with despair--there was so much screaming-til-you're-hoarse about nothing, and then once they've cooled off, they'd forgo any apology or closure and just try to forget it happened. It fucked with me. It made me hate myself and stuck me in a sort of emotional arrested development for years.

My parents are very sick people. They've lived a long life treating their anxiety and fear of being known with functioning substance abuse and hot-headedness--they do not, exactly, have a depth of emotional intelligence. I still love them, but if it were just me, I would keep that love from an Orlando-Augusta distance, at least for now.

But it's not just me. My sister still lives there.

My sister and I are different. I was by my parents notion "rebellious", but I was actually a nerdy homebody with not a lot of friends. I didn't do a drug until Senior year, didn't drink much. My sister, however, was totally rebellious. She'd cloud our house with weed, hung out with local fuckups and got into legal trouble, threw parties when my parents were away. If the fighting with me was bad when I was a teen, the fighting with her was straight-up emotional turmoil. It'd shake the house. At the time I'd just ignore it, which I completely regret. When it came time for college, she didn't move far away--she decided to go to a local college, and stay at home.

Now, every so often, she calls me just sobbing. My parents still treat my sister like a child. They rage at her for staying out late, for never being home, for the slightest instance of curtness or attitude. She never got the distance to clear her head. As a result, her grades are still bad, her motivation is weak, and I'm pretty sure she has no idea what she wants to do with her life.

I've tried to help. I've pushed for her to look into therapy, apartments closer to her school, a better part-time job, a major she can actually care about (she's going for some basic English major, but I know she wants to work in film). But I can't actually financially help her do anything. My parents, however, can. They'll give her money if she asks and then hold it over her head for months. They don't have any faith in her independence and have made that completely clear.

I've also tried defending her in certain fights. However, I've found my parents demeanor has changed since I moved. Now they're nothing but sweetness and affection every time I call, even if I'm angry about the way they've been treating my sister. They act like the exasperated, hard-working parents of a deadbeat lout when I bring it up, and quickly find a way out of the conversation when I plainly tell them they're being ridiculous.

I'm heartbroken. I don't know what to do. My sister is so smart, but I'm the only one telling her that. She's in the same state I was in when I was a teenager--a chronic self-hater who believes they're going to be a failure forever--but she never found a way out, and I'm scared that even if she does at this point, she'll be poisoned away from things like therapy.

Tl;dr, Moved far away from anger-issue parents when I was 18, immediately felt my self-worth improve, my sister is still there and the fighting has only gotten worse.

What do I do?