I agree that you can keep more then one tang in a tank. You have to consider all the angles as much as you can because each individual fish can also be different in its personality and aggressive behavior. When I purchased my tangs I did not totally do it on looks or a cretin type. I picked a bunch that I liked and slowly reduced it down to 6. There were many reasons I like ones that I took off the list but in my research I figured they would not be good candidates for a multiple tang tank for one reason or another, temperament or to similar shape or something. The list of tangs I have are as follows and they all seem to get along just fine. I have more aggressive stuff from my breading male 3 line damsel fish then any of the tangs.
Blue hippo
Bristle tooth tomini
Scopes
Vlamingi naso
Yellow eye kole
Blonde naso
This list may not work for everyone but I tried to also build a tank that would make tangs feel safe and still have lots of room to roam and even the biggest, vlamingi has places to hid, even when he gets to 1.5 feet long he will still have a place to get into. This is an important consideration when having tangs. They all have to have some place to hide to feel comfortable IMO.
