I have the following Tangs:
Hippo
Naso
Powder blue

The powder blue is a recent addition(about a month ago). The Naso and Hippo have been together for 5 years without any problem.

I have a regal blue tang, yellow tang, and a large naso tang in my 180.
Mostly the rule of thumb is to make sure they are not the same color or shape.
If you add them all at once u wont find them fighting over territory.
However a friend of mine has 3 yellow tangs in one of his tanks, so all rules dont always apply.

I have a powder blue (3)years a naso and a yellow in a 150 gallon.... never any problems..

I used to have in a 125 g reef system (listed in the order of introduction):
- Purple tang (very hardy fish the starter of my tank)
- 3* yellow tang (same size as the purple)
- Clown tang (introduced very small)
- Blue powder.

All were good mates !

BTW I sold them as a group and they still get along at the buyers tank!