What to do with a controlling sister?

I am living with my sister and cousin we pay rent and clean buy food and so on.
My sister was staying by her boyfriend for almost a month and when they have a problem she comes back home and want to put her stress on everybody.
She cleans by him she cooks she buys him and his brother a whole lot of groceries but when she comes here where she lives she doesn’t do all of that just complains.
Today when she came home she starts putting up letters about clean your own mess and a bunch of crap.
We have one fridge and she wants to be the boss on where to put what and how she moved my medicine twice and I move it back. It is Saturday and that’s cleaning day so me and my cousin cleaned not because she said so but because we had to and then she started bragging about a least we could read. I said it’s not because of you and she wants to argue and I must have said something bad cause my boyfriend was there and told me I shouldn’t have said that and what not.
And she was telling everybody that this is her house and I’m like okay why am I staying here if its your house, we all pay equal rent.
They contract is almost up and I am planning on moving but my cousin doesn’t want me to cause he doesn’t get along with her at all but I really want to.

What to do?