How do I learn to deal with my family?

I'm in my early 20's and I have to move back gone for a few months until I begin grad school in the next few months ::: I don't really have a relationship with my mom it's just her smothering me all the time:: I have a step dad that he does is eat all day and screams ::: I also have to see my obnoxious cousins who for the own reason always feel like everything have to be a competition :: and now I feel like my ex wants to get back with me and I honestly feel it because he may feel like he's losing me??? I just don't know what to do??? Any opinions???