One or two people at the same time.
The father can't take the girls.
The mother can't take the boys.
The thief can't be left alone with anyone except for the police.
I can get the father, the two sons, the police officer and the thief across but whatever I do after that they end up killing each other.
And something else, Can you pass the third grade? I can after a few tries. Do third graders really have to know that and be able to do it that fast?
Can you tell I'm bored and avoiding studying?