I keep a Green Mandarin Male, Red Mandarin Female, and a Target Mandarin. There is no fighting between the 3 of them. And they are obese. My mandarins are so well fed that they aren't even that active.
I miss having them cruise amoung the corals, mine are mostly settled on the bottom of the tank.
The oldest is 3+ years in the tank. The red Mandarin was added last about a year ago.
Dave B