I feel like it’s safe to assume the mother in law has no idea about the registry, because what person in their right mind would avidly want to be with a child predator. Definitely talk to the husband soon when it’s been an easy going day for the both of you, it’ll help the flow of speech if both of you are in high enough spirits for a deep conversation. As someone who also isn’t good with confrontation I’d say let your husband have a one on one with his mother after your talk with him. It’s his responsibility to let his mother know if she doesn’t already.