If you haven't got the time (lots of time!) to wade through the thread to which @Royal27 has referred you, I would say that based on my experience, you need not tip "extra" for someone with whom you are sharing a room. If your son has his own room, then a small tip may be in order to the housekeeping staff. As for cooks, etc., then you might want to increase your tip slightly, but not nearly by the amount which would be more usual if he was an independent hunter.