He has had a complete neurological and endocrine workup? i.g. fMRI, EEG, Labs?

Taking into consideration your mental health history, his present symptoms, and his winter birthday, he has schizophrenia or schizoaffective disorder; if he has prominent mood symptoms then it's schizoaffective disorder, otherwise it's schizophrenia. Since you indicated he has trouble with emotional regulation, I'll presume it's schizoaffective disorder. Has he ever suffered mania or depression that has lasted longer than two weeks?

I would recommend that you take him off the ADHD medications. I'm of the opinion that his ADHD symptoms are actually a subset of his schizoaffective disorder. Long term use of stimulant based medications can damage his brain and more than likely exacerbate his schizoaffective disorder. More then likely his stimulant medications is actually the reason why he is hearing voices at this age. Seriously. Work with your doctor and temporarily take him off all ADHD type medications.

Also take him off risperdal, otherwise he'll start having cognitive defects too. You'll want to try him on something like Latuda or Abilify. These are targeted specifically for things like schizoaffective disorder, and have less cognitive impairment. I really think if you get his schizoaffective symptoms under control his ADHD symptoms will go away.

There are supplements you can start him on, in particular you should start him on an antioxidant, as oxidative stress is a major factor in bipolar and schizoaffective disorder. I personally would recommend N-Acetyl-Cystieine and Astaxanthin.