Here's my concern...the other two fish developed immunity and are now "carriers" of the parasite. Meaning they allow the parasite just enough opportunity to continue completing its life cycle unnoticed. If they weren't treated thoroughly and then released into the DT, you could have actually reintroduced it and nulled the fallow period
My advice is to treat ALL your fish using a 75-90 minute bath in ruby reef rally (acriflavine, it's milder than formalin and not a carcinogen). During that time, I would break down the QT, give it a good vinegar scrub and thorough rinse, and refill with fresh saltwater. Then, follow-up with a 10 day treatment of metroplex and another 6 weeks of fallow time in DT.
I'm sorry, I know it's a pain, but without full treatment you risk re-infection with any new fish you add. It would be a shame to do all the work of QT, just to have them catch brook in the DT...