Look into public housing. Does he get ssi? Is he on meds? seeing a therapist? It sounds like at the very least he needs partial hospitalization. If the threatens suicide call the cops, each and every time. Your parents shouldn't live in fear. Can you and your parents foot the bill for a cheap studio until he gets hud? It can be in a shady area, and an hour away because it doesn't sound like he goes out often. Your parents need to set rules and get rid of the cats(or not allow them down there. Get them a mini fridge. He needs professional support to grow out of the teenage years. Clean his living area and treat him like he's five. Who has to clean his room weekly.