He should take his wife across first then go back and get one of the strangers. After he drops off the first stranger on the other side pick his wife back up and take her back with him. Then drop his wife back off on the original side and pick up the second stranger. Then drop that stranger off on the opposite side and go back to pick up his wife. Then they go back to the side they need to get too.
He should take his wife across first then go back and get one of the strangers. After he drops off the first stranger on the other side pick his wife back up and take her back with him. Then drop his wife back off on the original side and pick up the second stranger. Then drop that stranger off on the opposite side and go back to pick up his wife. Then they go back to the side they need to get too.