I Have A 19 Year Old Nephew How Has A

I have a 19 year old nephew how has a hard time communicating, paying attention, does not like to look people in the eyes unless he is perfectly stoned. He obsesses about weed and once he is too stoned turns into a zombie. I have showed him many times how to put the dishes away but still does it incorrectly, that is just one example of small things on a daily basis I have been dealing with. My niece is on the asburgers spectrum, do you think he is as well? My son who just turned 16 seems way more capable then this child. I would love to know your thoughts. Thank you for your time