If you want others to be mild to you, be the same to them first.

I would tell him show the example yourself. I can't find the saying in English... My father was smoking years ago. Then one of my brothers became also a smoker. My dad would have liked to see him quit because he knew it was bad. But he said he could not tell him that because he was doing it himself. He tried many times to stop smoking but failed. Well Finally they both quit... For Brad to teach his younger sisters/brothers to have good manners, he should start behaving good himself.