It sounds like they have already made up their minds and that NOTHING you would tell them would change their minds. So why humiliate yourself by trying honey? Dad obviously has already projected onto them that you are a liar and that anything you would say about what he did would be a lie. If they have a relationship with their father then why are they punishing you? Where is the forgiveness? And if you didnt remarry what sin have you committed? If this man is a child molestor I sure hope he doesnt have access to any grandchildren as hideous and heinous as that may be.
If there were no police reports about the abuse then its his word against yours. From where I sit, if you just say "I love you, I have always and will always love you. You are my child. You have to decide what you want to do with your relationship with me, but I will not discuss personal matters with you that occurred between your father and I. I chose when they happened to protect you from them, and I choose now to protect you. He knows what he did and I know what he did and God knows what he did. I hope someday you will see your way clear to talk to me, to forgive me for what you perceive as my sin...and that we can be a loving family again."