HOV south on 75 till 635. Then it's a 30 min drive to downtown. If traffic looks bad on the map, ill take 175 to I20 and cut over to 35 south. It's a couple miles further but typically less traffic. Either way, when leaving at 5, it will take you 45 min to an hour to get to 35 and 20. It should start to unravel just a few miles south of there.
Good luck to you and your nephew. Hunting south tx is hard to beat.