Is maintaining ties of kinship obligatory with an abusive father who molested his daughter, then tried to photograph parts of her body while she was asleep, and now wants to communicate with his granddaughter despite his daughter's and her husband's refusal?

You must be kind to your father, maintain ties with him, and not cut him off or prevent him from calling your daughter or seeing her, except to the extent that protects you and your daughter. For a father has a great right over his child, and Allah has commanded companionship with parents in kindness, even if they enjoin polytheism. It was reported from Ibn Abbas that there is no Muslim who has two Muslim parents and wakes up to them seeking reward except that Allah opens two doors of Paradise for him. And if he displeases one of them, Allah will not be pleased with him until that parent is pleased with him, even if they have wronged him.