Daddy problems

And no im not talking about my baby daddy im on about my father. He is having a baby with his whore of a wife and I haven't seen him in 8 months and if im honest I wish him 8 feet under coz of the horrible things he has done. However he has said I can only see the baby if he is there and I cant see the baby without him. And I cant walk out on my unborn sister but I dont know what to do. Please I need your advise on this.