Brandon,
How big of a tank do you have? That is a lot of tangs. One of the easiest way for your fish to get ich is by being stressed out. With that many tangs in a tank that may not be big enough, the ich may be difficult to get rid of.
I would definately try garlic. The easiest garlic to get comes in a drip bottle, Kent's garlic extreme, you can get at any LFS. When I use it I drip some on a piece of nori, then feed my tangs. They love it.
As an alternative, I know people on the board have used Marine No-ich with some success. Just search around the message board for more info on this subject.
On a side note.... sometimes what your wife wants, (or even you want) may not be what is best for your tank. My wife loves angels and butterfly fish, but they are definately not best for my reef tank! I really would like another Powder blue tang, but I know they are difficult to keep and probably wouldnt survive in my tank. I hope your regal tang makes it, but you may want to do some more research in the future before making a purchase like that.