Damn, I think you're right. Just how many Penn's were there?
Besides Sean, Chris and Michael, their father Leo was also famous in Hollywood. He directed for some enjoyable family shows such as Little House and Diagnosis Murder, but I understand that he was a radical leftist/communist. That would make the Penn brothers red-diaper babies, which makes it kind of inevitable that Sean would turn out the way he did. Not saying it makes me like or feel sorry for him for having such views, but he was born to it.
Never knew anything political about Chris, and enjoyed him in the few movies I saw him in.