I wouldn't worry too much about it. It sounds like you've nailed the problem right there: the hot water and the lack of conditioning. If your nephew gets started on a regular conditioning routine and cuts down on the hot water on his hair, he should be okay. At that length, it's easy for him to "redeem" himself to his hair. And if anything, he'll have a fresh head of hair after a month or two anyway.

If you're worried about his scalp and hair, maybe you can talk him into a deep prewash oiling treatment. A heavy oiling with coconut oil or another cheap affordable one. Then he can shampoo it out in the sink with warm/tepid/cold water, and condition of course, before actually showering.

Anais