My Son Has Schizophrenia & He Is Taking A High

My son has schizophrenia & he is taking a high dosage of Seroquel. His siblings don't realize the drug may affect his ability to stay focused, clean his housing or feel comfortable around them. When he visits his M.D. his brother is always in the session so he does not have the ability to speak about wanting to lower the dosage. I am his Mother & he was diagnosed @ age 16. He did gain weight but now walks 8 to 10 miles a day. thank you for any insight.