Thank you for that. I do treat my fish in qt. I do not just monitor. The method I found best for my fish depends on the fish itself.
So, me, I would proceed as follows.
If the fish is eating consistently and not showing terrible signs of velvet/brook I begin an antibiotic treatment. I use the Triple cure from Everything Aquatics. I do a full 10 day treatment. Then I will use formalin over 6 days (1ml/10g dosed every other day - 3 times). Then I observe and feed a medicated food with parasite control (same company). I will use prazipro if they hate the food, but so far fish have eaten it fine. After about 1 week, no issues, they are done with qt.
Now, the last round of fish, I used CP in the 60mg/gallon dose for 14days, then the parasite control food/prazipro. The fish were healthier than the batch I got and treated with antibiotics first. I worry about the lack of appetite in sick fish with CP.
Now, I do give acriflavin baths when they first arrive (not sure if this has had any effect, but no harm either).
I have never used copper and probably never will. I know others do just fine, I never wanted to deal with it.
For your fish, I would follow the bacteria treatment first then deal with the next CP/Formalin/Reef Rally type meds. The reason is I do not see any indication in the pictures of a critical issue (covered in ich or velvet or sores). The fish will get its immune system up to par and hopefully felling better on the meds. Then, you can hit them with a more invasive med.
I have really liked the Everything Aquatics meds. I have used the triple cure powder and flake food. I have the anti-parasite flake and even the CP flake. I have the acriflavin for baths from them and the CP (when it was available). They make the meds after you order, so they have a long shelf life. Takes longer to get meds, but I like that they are made when requested.
Formalin I got on
amazon ( 37% UPC lab grade formaldehyde ) and it is very short lived. It is not effective after 6 months. Keep an eye on that.
I hope that makes sense. I wish you the best on this rescue.