OK so I just recently moved in with my brothers girlfriend and another girl. And my brother lives there most of the time too. And they are driving me completely nuts!! My brother and I are really close but whenever he's around his girl her attitude pisses him off and he takes it out on me. And he gets mad when I don't come home or am out late. But I am 20 years old and have a life and a boyfriend, plus he's younger than me trying to act like my parent. His girl does nothing but whine! She can't even walk in the dor after work and say hi to him. She walks in a whines the she's tired. And when I say whine I mean WHINE! The other roommate doesn't cook clean or help out around the apartment in anyway. I can't stand a messy place where I'm living. There even has been a couple times where I'll be cleaning and both my roommates will be standing there watching me. Plus my brothers girlfriend tries to act like my mom and if I'm not home when she thinks that I should be I get calls and texts asking where I am and who I'm with and when I'll be home. I just want to live my life my way and not answer to anybody that's why I moved out of my parents house in the first place. I want to tell then all to f off but I don't want to ruin my relationship with any of them but mostly with my brother. How do I tell them that I'm not happy with how things are going without coming across as bratty?

You live with them so I think you need to find ways to adjust or just look for another place.
To adjust you could tell them beforehand that you are going out with your boyfriend on Friday night and don't expect to be back before 3 am. If they still bother you with phone calls and acting like your parents then it is a problem that you may have to find even another way to deal with or move out.

Until you are able to pay your own way, in full, without help from anyone else, you are always going to have to compromise.

It is just a fact when anyone shares a residence with another.

You can decide how much to put up with, and when the limit has been reached, you can find some other place to live.