I don't know what's good enough for them
Take the kids away from them, for sure, but I don't know what the hell kind of fitting punishment you can inflict on someone deliberately doing their best to conceive children with birth defects. It's one thing to have a genetic risk factor but try to have children; it's another to *try* to create birth defects.
Famous last RPG quotes: "I'll just shoot this fireball down the dungeon passageway..."