I would use melafix - I've had great success treating finrot with melafix. It should be safe for your catfish. Check the notes on the bottle - it should mention if it's unsafe for sensitive fish.
Just an update. Angel (the first posted) is doing quite well although still upside down but not red sored at all. I tried one harness..didnt work but have plans for another to try today I still have to hand feed her but I dont mind at all. Shes so sweet
Claudius (second posted about) is doing much better too. The Melafix helped and he seems to be healing now. I did a week of it and his blisters disappeared and his fins are growing back