How can I stay in the USA after I finish college?

Next year I'm going to the USA to study Theatre Arts. The thing is I'm from Venezuela and I would like to stay and work in the USA after I finish college. I know you can get a greencard if an employer sponsors you but that is difficult in Theatre because employers usually choose an american citizen/ someone with greencard because it's easier, plus there are a lot of talented people out there to employ. Just in extreme cases where no one seems right for a part they choose the foreign person. I have an uncle and an aunt who were born in the USA and I was wondering if I could get the greencard if they sponsored my mother (their sister) and she got it. Is it difficult to get the greencard through your brother/sister?