How do I become less irritable around my parents?

Warning this is a bit of a trauma dump and a very long text thread ahead

I know the reasons I don’t get along with my parents. I moved away as far as possible for college a few years ago, now I only see them every once in a while.

When they’re away, I speak to my mom on the phone pretty often, probably most days and everything is fine. When I meet them in person it’s a completely different story. They are not bad people, but I have always been different from them and they never really quite understood me. They have been very open about seeing me under a mostly negative light my whole life. The prime example to this is my mom who keeps telling me I’m exactly like my dad, which is hard to hear because he had a long run of domestic abuse with my mother. Throughout my childhood I witnessed this domestic violence. 

I confronted my dad about the resentment I have for him, but he only runs away from taking up the responsibility and tells me that I should not make him pay for his behaviours in the past because he’s now changed. He also insists that he used to beat me as a form of discipline because he was ignorant and misinformed, which I believe. But it still doesn’t really cover for the violence against my mother. I have disliked my father throughout my life, he is  hyper critical and thinks he’s a know it all, believes I owe him my life now since he’s been financing my education, downplays my struggles and is still emotionally/mentally abusive ofcourse but way more subtly. 

In spite of all this, I still don’t view either my parents as bad people, but all this resentment bubbles up when i’m around them because I’m triggered into the childhood I very much hated. I end up super irritable and snappy, and I feel really guilty after I do that because they are trying to now love me. I don’t like being angry, and I almost forgot what anger felt like before having met them again after a year and a half of living across the globe. It makes me feel really emotionally immature and I want to stop but I can not seem to stop myself from letting my emotions get ahead of me when I’m around them. This is not a problem anywhere else for me. I’m a very calm person all around (my parents would describe me as “slow” or “cold”) but it’s almost as if their presence triggers a little angry demon in me that I otherwise forgot existed. 

I feel like this attitude is making them resent me slowly now, and it’s making our relationship harder to repair. They don’t believe there’s an issue with them. They believe I’m snappy and need to respect them more. 

I don’t want to feel like I’m fighting my way into getting their approval again, especially as now that I’m older I recognize that they are the type of people I would have vehemently avoided had they not been my parents. 

I don’t want to completely cut them off, partially because they have no concept of boundary and wouldn’t take me seriously anyways. But I also don’t want to lose contact to my sister, and I’m trying to mediate to avoid any further explosive arguments (which would be the result if I tried to go no contact). 

I don’t know what to do. I’ve been confused about this my whole life. My emotions are a rollercoaster and every hour is a different feeling towards them. How do I deal with this? Any advice on how I can make it work with boundary-less parents without going no contact? I just want to get along with them, and they don’t see my effort but it’s still worth a try.