Welcome to R2R!
I presume
@Jay Hemdal will recommend CopperSafe if available, over Cupramine for your copper treatment(s).
You have my sympathy for taking on too many tanks at once. And yes, it does sound like you have been cross-contaminating tanks. It's easy to do so don't beat yourself up about it. Just take it one tank at a time and remember that failure is defined by quitting, not by determination.
Here's my short list of handling sick fish when all goes to h--ll at once...
* Monitor Ammonia carefully and be prepared to quickly do water changes (with meds pre-mixed) if it spikes. Seachem Ammonia Badges are your friend.
* If you have an easy source for freshwater dips, that can be a way to buy time for the fish while you get QT tanks and meds ready.
* Use heavy aeration whenever possible in combination with meds. The fish need it more during meds than any other time.
* Make double-triple certain you don't have any Carbon or UV running in the med system(s), as either will negate or even toxify your meds.
Good luck, you've come to the right place for help.