You will get completely different advice. My 2 cents is that if they're smaller tangs, added roughly at the same time, and your system is and remains ich free, you can pretty much do whatever you want if you have several tangs to spread aggression. I break nearly every tang rule there is, but I also have a lot of experience, I have a plan B when an issue arises, and somewhat know what I am doing.
For example I keep two powder blues together. They're also with an Achilles and powder brown tang. No issues. But the real reason I think it works for me is I got them at the same time, they're all pretty small, and I have several other tangs, too. Chevron, purple, Sohal, Desjardini Sailfin, and yellow. Lots room to "spread" aggression.
The other thing to realize is that tangs are nitrate factories. They pollute your water heavily. With lots of tangs comes expensive skimmers and other filtration, frequent water changes, and vigilant quarantining to prevent illness.
I don't recommend people do what I have pulled off. What I didn't tell you is that I've had to sell a few tangs that were problematic to find more docile specimens to get along. It's not been a bump free ride.