Royal, NEreef is right. Tangs really should have at least 48" of swimming room in a straight line. I wouldn't get any tangs for that tank. If you want a yellow fish I recommend one of the yellow dwarf angels. They look just as good, but they don't need as much room.
If you put 3 in that tank, there is really very little chance ANY of them will live long term. And once one dies, your whole tank will be at risk. Especially since you will have the even # you mention which will likely fight to another death. Really, in a tank that short in length I wouldn't be surprised if none of the 3 got along because there isn't enough room for territories.