Mine used to do the same to BTA's. If the Duncans can recover on their own without too much trouble, I'd let it go. If not, you might want to relocate the Duncan's. My pair are hosting in Duncan's now, too, but haven't done too much damage (a year or so now).
Maroons are very personable and can certainly tick you off more than most others. Cinnamon's are a close second in aggression. They can sling rocks many times their size and don't think you have any idea how a reef should be decorated. I lost my first female (had her 12 years) when I moved to my current location. Of all I've lost, I miss her the most... She'd attack every time my hand went in the tank, and even when I'd see her coming, I still always jumped. She was the third fish I ever bought (following a pair of electric blue damsels-all the rage back in the day;)).