I don't know how to say this in a nice way, so I will just be blunt.
The worst thing you can do is have one foot in one solution and one in another. By now you should be close to therapeutic copper levels, and have a fishless DT for a week now. Are you using cupramine? What copper are you using?
We mentioned from day one that you needed the ammonia badge, not to use ammoni detoxifying products, etc.
You aren't committed to a solution and your fish will and are suffering for it. The fish in qt weren't exposed to a therapeutic dose yet. They were basically set in a strange tank and stressed out while still being eaten alive, of course they died. Stress kills but if handled properly it's the path of least resistance with an infestation as you describe and with fish you wish to keep. (So long as there is a therapeutic level of medication present)
Much advice appears to have been overlooked. You didn't do any dips to relieve fish prior to going in the DT which was also suggested so that it may provide immediate relief until you got copper levels where you needed to (therapeutic levels).
You aren't answering critical questions so that we can assist you. You're taking advice from several people with conflicting views, which is fine but pick one. Being on the fence at this point has likely costed some lives of fish and certainly unproductive time you could have spend towards the end goal solution.
I'm sorry to be short, I know it's confusing, difficult, irritating, and there is a lot of conflicting viewpoints. This is just not something that you can afford to be "wishy washy" about. Pick a solution that people you trust and feel have great experience and track record put forth (and you trust). If that isn't what we suggest, fine.
We are trying to help you.
Again, I am sorry if I upset you with how I said this, but IMO it needed to be said. We don't think any less of you, we have all been there. You just need to fully commit and act, and do it quickly. Halfway doing anything only makes the problem worse. Done properly and everything taken note of, gives you your best chance.
There are copious threads that are scientifically and experientially/anecdotally supported that have been provided here and are available to read on R2R.
I have thousands of dollars of fish, I don't even want to admit the total value of my collection because it's embarrassing. I didn't get here and invest in these fish without a clue of what I am talking about. That said, there are plenty others wiser than me. Let's rock and roll and save as many fish as possible. They've all been infected so long it may be too late for many of them but let's work together to minimize stress and losses. Most importantly, let's learn from it!
We've all learned expensive and sad lessons from mistakes. I wish you luck buddy let me know if I can help with whatever you choose. I'll continue to try!
This above to the 10th power!!! Everything has been said several times and you still ask the same questions (fw dipping, copper levels, remove all fish, ect), we get that you're in panic mode but either pick one of the solutions offered in this thread or one of your many other references! Every time something is offered, you seem to want to counter it with someone else's solution, you've wasted so much time waffling that your specimens are suffering because of it. Pick one person to deal with and live with it, I've done just about every method that's been suggested and they all just about worked every single time, and I always install a UV on every system as long as it has a chiller on it. Good luck.