That's your wife.  According to the vows you took, your wife>your kids.  IF I was in your shoes, I'd slap the fuck out of the kid who treated my wife "like shit", no matter what his age.  And if he was 18+ and did like it- hit the fucking bricks kid.   
You have 18 years to get it right, or at least set them on the right path.  If he/she still fucked after then, it is what it is.  Let them figure out their way.