Wow.
To his credit 21 hours a semester is A LOT of school. If he is making decent grades, that is a plus.
However, why is a 20 year old young man living with his parents and disrespecting his mother in her home? That is not good. If he is leaving this summer, then his daily antics will no longer be waved around in front of you. Can you detach until he leaves? Can he be out sooner? You can no more control your father's and husband's interaction with their grandchild/son then you can control your adult son. I would keep reminding yourself of the serenity prayer.