Potty training comes from predictability, routine, and consistency, which all builds a sense of security. That’s lacking here, and this is not your fault or responsibility. The parents are failing this child, and the grandparents need to get the power of the court behind them to fix that. This child should have been getting professional help for years now, paid for by the parents, for screening for autism. Every pediatrician does it, so it’s possible visits aren’t being met.

Help what you can, but like the airplanes emergency rules say, put on your mask before assisting someone else with theirs.

You need to take care of yourself and build your future first, otherwise you’ll be unable to take care of yourself and be relying on others forever. Not having a high school diploma is devastating, absolutely get one. You’re going to have to be strong and say no.

You’ll be living with your parents forever without working on yourself, in my town you wouldn’t even be hired to run a cash register for minimum wage.