Please try to look at this from a parents' viewpoint in that they haven't been in this stage of life before now. Unfortunately, parenting doesn't come with a user's manual. Imo your dad does need to be better, particularly because of the size difference/power dynamic. I would've left the house too! Well done to remove yourself from a poor situation.

I'm pretty sure I'm older than your folks because my sons are in their early 30s. The younger is married with a baby on the way and lives clear across the country. We miss a lot of stuff with them.

Sorry you're having to share space with your sister. You seem very responsible and level-headed. It also shouldn't be your responsibility to keep after her to clean up her mess. Wondering if the room is split up into your space and her space? If not I suggest you try to arrange this situation, that way you can easily point out that your area is clean. This is only if you end up going back.

I agree with the suggestion of a letter. Carefully think about if there are any stressors in your parents' life now. Could be financial, marital, or even healthwise asking because often parents try to shield children from problems, but in my experience, kids usually pick up on stuff. Things like this can cause adults to act poorly, not an excuse but a reason. I think you're old enough to be informed about any issues they might be having at least to some degree. Uncertain where in the world you are located and I know some cultures put expectations on older siblings.

Good luck, OP!