Not all tangs are agressive contrary to rumors. The non agressive tangs are considered as:
Orange shoulder, tennenti, bristletooths, hawaiian/blonde nasos, achilles tang
The aggressive tangs are: clown tang and sohal/red sea tang.
The rest of the tangs such as purple, yellow, powders, blue regals, etc fall inbetween with some being teddy bears and some being lions.
What is in your tank? How big is your tank? Just add the tangs in at the same time and nearly all the non agressive/in the middle tangs will all get along just fine. There agressiveness comes out with shortness of food and trying to add more tank mates after the have set territories