You will never be able to have any tangs reproduce in an aquarium... The "captive bread" tangs available, were eggs in the ocean, placed into an aquarium to hatch.
Tangs get together by the hundreds, and swim around each other like a big "cyclone" in the water, this is their mating ritual. Then all at once, hundreds of tangs release eggs and sperm into this cyclone. Many of the eggs are fertilized, and they drift off, hopefully settling and hatching undisturbed.
I suppose that it is possible that one day with a HUGE aquarium, this action could occur and produce fertilized eggs in captivity, but its very unlikely.
As for the hybrid question, I'm not a bio major, but i'm pretty sure as long as 2 animals have the same # of chromosomes, its possible. Also, RandyO was holding onto a hybrid tang a while ago. So its most definately possible. In the cyclone event, not all the tangs are of the same exact type, but I think it would be mostly yellow, or mostly hippo, and so forth...
Your tangs are probably fighting. There might be a lack of algae to eat... Try feeding some live crap algae to them--you could harvest it from another place-like a fuge. Also, you could try massively redoing the aquascape, confusing the tangs into liking one another...
Steve