my stepmom is mentally harassing me..

Im 20 yrs old now.When I'm 3yrs my mom gone from us.I have an elder sister also.My father married another women when I'm 6yrs.After they have a boy.Then my step mom started behaving badly.She started blaming grandmother,sister and me to my father.My father did all the things for step mom and step brother. He done nothing for us till now.Grandmother was the one doing all the things for us.she was doing things equally for 3 of us.Step mom blaming us all day till now.Father doesnt care about us.he hears and does what she says.Sometimes I lose my control and will say something against this situation and that again make problems.i realised father doesnt care about us.so I stoped saying things to him.Last year he had stroke and he is not able to walk even now.Step mom is being more cruel to us.she is continuing blaming us to father.he doesnt care.all day I have to hear this sitting in my room.it makes me bad..i dont know.i hate all.what can I do?There is no one beside me to say a word.