As I said, I've only heard one side of the story. There could be a real - as opposed to just plain spiteful - reason the father doesn't want the other kids with their grandmother. My opinion, based on brief conversation with the Grandmother, is that Lee-Lee is with someone who loves her and who will be able to help her through this terrible time in her life.
But if it is just out of spite - well, one day he will meet his maker.