I am so sorry. But there really is no solution that I can think of WITHOUT taking him to a vet first. The two most common reasons for a cat to pee outside the litter box are UTI (urinary tract infection) and crystals......a urinalysis would test for these. YES, it could be behavioral, but you can't begin any treatment without knowing.

So the best way for you to help is to convince your parents to at least try urinalysis. After all, urinary tract problems cause pain, and won't resolv themselves.

Good luck.