What does everyone think i should do?

Ok well heres the story: My dad kicked out my mom when i was like 2 cause she cheated on him but what we didnt know was my dad was cheating to (terrible i know) anyways now i have a stepmom that always gives me dirty looks and doesnt care bout me or anything but herself and her daughter,, She made my dad hate me with her stupid lies and now my grandparents believe her to and i have no control over it. Anyone have any suggestions? I hate her so much! Shes always hapy when my dad gets unhappy with me! :@