He may have defenses, but not notifying his parents or taking him into custody without a parent is not one of them. He does need an experienced criminal defense attorney to represent him.
YES. Your question has a lot of sub questions; your nephew needs to speak to an experienced criminal defense attorney immediately. If his parents can't afford to hire an attorney they should apply for a public defender immediately. Your nephew should not speak about tthis to anyone until he has spoken to a lawyer. Good luck.