I'm in a conundrum with my living situation. Long story

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I'm in a conundrum with my living situation.
Long story short, I'm living at my parents' old house for the rest of the year, along with my sister (and her boyfriend, who doesn't live here but is here all the time and keeps all his garbage car parts here)
The problem is, they live like niggers, and I've been cleaning up after them for a year now.

We have assigned rooms that are our "areas" , and the kitchen is a shared area. They leave rotting food sitting on the kitchen counters, in the fridge, and will do insanely niggery shit like stuff the garbage bag until it breaks on the bottom (which I have to clean up) instead of just taking it down and putting in a new liner. They also have car parts and garbage and rotting food just sitting all over my side of the garage (their side is occupied by a piece of shit junker car) and they get away with it because they'll clean and throw all their shit in my sisters' office (which is basically chris chan's house levels of unenterable) the day before my parents visit. I've shown my parents photo and video proof of the rotting food, they can smell the fungus in the kitchen, and they haven't done anything about it (Keep in mind they are trying to sell this house this year.) I've tried asking my sister nicely to clean up after herself but she just has this thing she does where if she is criticized in any way she screams and throws a tantrum.
I'm sick of this. I feed her dog and pick up its shit in the back yard. I do all yard work. I take out the trash every week. Every single chore in this house is done by me. I do their dishes.
How do I get my parents to get them to change or get them the fuck out of here?
Right now there's rotting pizza crusts in the sink and on friday night they splattered macaroni and cheese all over the hall closet door, wiped it halfway off with a towel, and threw it down the stairs into my area.
I'm going to fucking murder them with a gun which I have if this doesn't change.