How to deal with a messy roommate?

I live in a 3 bedroom house with my roommates who have 2 children. I understand kids are messy, but its a little crazy. I work a full time job, my boyfriend works full time as well, my two roommates on the other hand, only her boyfriend works. She is home ALL THE TIME. So I don’t understand why there are molded dishes, food molding on plates in the living room, and clothes all over the house. And my roommate acts like it doesn’t bug her, when I talk to her about keeping the house in order she tells me ” we aren’t trying to impress anyone” yet when anyone comes over they call me and say we need clean the house.
I’m so tired of picking up after everyone. Her boyfriend refuses to do anything about anything until he can’t stand the smell.
Another issue is that her boyfriend only pays half of the rent while my boyfriend and I pay for half the rent, power, water, all of our Netflix, and the internet. So, the least they could do is keep the house clean…