Ok, not likely brook then but I wouldn’t discontinue the metro/prazi. You could do the copper with it, but like you said then you’d have to dose the water change water with copper and keep a steady eye on the copper level.
It could be a mild bacterial infection, though at this point I think I’d focus on continuing your efforts to get them eating. You could give them a 90-minute bath in ruby reef rally (acriflavine) and see if that makes a difference.
As far as getting them eating, it’s my favorite time of year... roe season! I’ve never had a fish refuse it. If you call your local seafood markets they might have some. Just freeze the entire egg sack and cut off slivers to feed. I use an algae clip to hold it.