What kind of lighting do you have on your aquarium? If you don't have the appropriate lighting for your coral species that could be a possibility for why they are not making it.
Also, I believe that Bristleworms aren't necessarily a bad thing, I hear they actually work as part of the clean up crew. Just DON"T GET STUNG by them (wear gloves, still may be stung with cloves though too).
Lastly, I hate to be the bearer of bad news, but your Yellow Tang needs a minimum of a 125 gallon tank.
If you have any further questions, just let me know.