I agree that Sarah and Ant are the two most likely to know the true nature of their marriage. Let's take Ant's impressions with a grain of salt, but he characterises him as weak and cowardly. Sarah was comfortable enough to tell the world her mum went ballistic, to me this suggests that she found her Dad's story credible at that time. Even if you loved your Mum, if you knew she was capable of giving Dad a really hard time and one day Dad snapped uncharacteristically, I don't think it is a stretch that you would get invested in protecting Dad afterwards. They both would have been better off coming forward immediately and letting justice take it's course. He would of been out of jail in time to be a grandparent to Sarah's children. It is not like it is going to interrupt his amazing career as a failed businessman and uber driver and lose the family fortune. They have to live with this hanging their heads while they disrespect Karen's memory and remains. The facade is cracked. They need to just get on with it, do the moral thing.