It may help your brother to do a parasite cleanse, look at some of the more popular kinds - Humaworm, Paragone. etc. They will have a program kids because they are smaller and need lesser doses. It would be best for your whole family to take the treatment and your pets, too.
From what you describe of your brother's problems he needs to be tested for gluten sensitivity. Gluten is a protein found in wheat, barley, rye and sometimes oats. Many of us have a genetic predisposition to develop problems with gluten, not all people develop the problems but others do when exposed to some environmental factor - stress, gastrointestinal infections and other stresses. A Dr. would order a complete Celiac Panel of tests.
Let us know if your parents are willing to allow the parasite cleanse and tests for CD. See 'The Gluten Syndrome' website. Getting rid of parasites is a good first step.