Your Grandparents don't hate you? Why would they? Just because your parents were young when they had you, and your grandparents may have disapproved at the time - it does not mean they hate you?
Your Dad really sounds depressed and like he has lots of issues! - I rewally do empathise with you here, we all would love to help - so please do not feel like you cannot open up; you can tell us anything - we will not judge, and there is no need to feel embarrassed - we just want to help!