What should I do in a toxic household

I have lived in a toxic home since childhood. But as I grew up these things became even worse. There were daily fights and arguments. My mother and father never understood me. My father always criticizes me. If there is a fight between my mother and father then he always tries to hit her and abuse her. They even says go and die or I'll kill you. Leave the house right now or I'll leave. Even my grandmother doesn't support us. She just takes my father's side and says "Ghar ki baat hai beta Ghar me hi suljha lo." And always blames my mom. My mom and me we both thinks that my father is having an affair..we are not sure but somewhere it is. He is totally changed..always talking about that another woman..criticise us and appreciate her child and abuse us..doesn't even talk properly. He always says "pata nahi bade ho kar kya karenge..mai to sanyaas le lunga ya to iski shaadi Kara ke bhej dunga" I'm just 18. I don't know what to do he doesn't allow me and my sister to go out..we always stays at home locked..my friends tries to request but they always say no..and says"padhna likhna hai nahi..bas ghumne ko chaiye". I'm so fed up with my family..and sometimes I just wanna die but I can't. Please tell me what should I do.