Well I say he's a punk but he was probably doing things like STAKEOUTS and saving kittens from trees and getting hurt a lot from trying to teach bullies a lesson... He was a very active kid so trouble also tends to follow. Oops. It sounds like this whole family would just be very, very supportive of each other. Misaki would look after Mao and his mom a lot too, and cover for Mao if he needed it!

why are they such good boys

I think Misaki would let Mao call him Misaki! He's just trying to avoid getting called nicknames he hates... But ah, Mao's growth spurt. He's proud, but also a little envious...