Have you ever had a family like this?

Wow. that's a hard life! First of all, it shouldn't matter what happened between your parents, grandparents and cousins. You are you and you have the right to have a relationship with your relatives even if your dad doesn't have want to communicate with them. You said you were young when your grandfather died and that was 21 years ago. I'm making the connection that you are no longer a minor. Having said that I encourage you to make contact with your cousins, aunts, uncles and grandma. If you want to make that bond you have to try. Don't be offended if at first they are standoff-ish, because they are going to be cautious. You need to make your own opinion for yourself, not based on what has happened or what did happen.