I think you should continue fasting. You are awesome, fasting at age 16. Also you have done amazing job in losing 40 lbs.
Romain lettuce, tomatoes, carrots, cucumbers are much cheaper than lot of junk. Your parents are buying packaged foods because it is easy for them. You have some educating to do with them. You can go shopping with them and add your own items to the cart.
Best way to brake a fast is with freshly squeezed orange juice. Ask your mom to buy three oranges. Grapes have lot of sugar, I would avoid it. Also try grapefruit, tomato, or watermelon.
Your diet after you get back to school sounds fine to me. I have never had chicken in my life. So don't know about that. Why eat something dead when you can eat nature made things with life intact in it.
You are on a good path, don't let anyone discourage you.