Oh Jeannette, I'm so sorry! It must hurt terribly to see what's going on and not be able to do anything.
I have been keeping my 8 year old nephew after school for the last several months. I'm trying really hard to help him, he is obviously having issues but there is only so much I can do, not being his parent. My sister lives with my parents and pays child support because my nephew lives with his father. His father makes a lot of money, and has several rental properties in town. He moved into a studio apartment with my nephew to save money. They share a bunk bed, the whole place is no bigger than my living room. No real kitchen, they have a microwave and a hot plate. They live right by the elementary school, and my nephew walks to school. I found out that he was walking home every day, and staying by himself until his dad got home around 5:30 or 6:00! An 8 year old boy doesn't need to be by himself for that long.
My sister and her ex are both very immature, and my nephew is starting to have behavioral problems, nothing too serious now, but if it remains unchecked I can see him turning into a very angry and destructive teenager. They spend more time trying to piss each other off, than actually interacting with their son. And now his father is using me for child care, he actually took off of work the other day and flew his power para-glider on the beach for 4 hours while I kept his son. He always says, "I don't want to impose, if you can't watch him, I'll just take him with me." Yeah, right. Leave my nephew on the beach, BY HIMSELF, during SPRING BREAK, while you're thousands of feet in the air.
Sorry, that took off for so long. Didn't realize how angry I was!
Good luck with the in-laws, keep doing what you can for your nephew. Hopefully, they will realize that he needs some help and take him to the doctor soon.