I can understand you having problems with the Kole and Bristletooth, but the Sailfin I would have expected should have been OK.
Maybe you should review where you are buying them from.
I've posted previously that I bought a Kole tang from a shop and that after that my tank got white spot when I'd never had an outbreak of whitespot before. I am dubious about one or two shops. At another, they actually told me they were going threw a white spot phase and therefore they could not sell me any of their fish at that time - this I think was admirable of them.
I previously got a lovely sailfin when I first started keeping saltwater fish. I got it along with live rock from a fellow aquarist. I had no intention of keeping it, but the seller of the live rock insisted I take everything. It had the best character and would always be at the front of the tank looking at me. But, I sold it on as my tank was way too small for it. Point is though, before I sold it the tank went through a cycle and the sailfin had no problems at all. Seemed to me to be a hardy fish.
I'd had no experience with Whitecheeks.
I currently have a two spots tang also and it seems pretty hardy. I will be selling it soon as it's housed with a yellow tang and as the two spot is getting bigger it's also getting attitude. My Coral Beauty can no longer boss it around and it's been picking on my Strombus Snail - using it's tail to swat the poor strombus.