The criminal people don't need to stay together, the thief can stay behind as long as she is alone. You can hence use the policeman to ferry a son/daughter. The

The criminal people don't need to stay together, the thief can stay behind as long as she is alone. You can hence use the policeman to ferry a son/daughter. The next challenge is if you go from there and ferry one side of the family across, eventually the boat will be on the wrong side - so you need to make a little tedious shuttling/shuffling session to make sure the policeman/thief duo actually waits on the opposite side. From there, it's pretty straight forward again. I'd say those are the only two critical sections, the rest should follow automatically.