These two synos look absolutely plastered in Ich, just like how I found my six youngsters a couple of years ago.
I would use a divider such as the Penn Plaxx to seperate the two of them in the tank they are in, if you are sure they are fighting*, otherwise you are spreading the Ich to other tanks and fish. Did you supply these catfish with numerous caves/pvc tubes to roost in during the day? Ordinarily, that would be the only reson for them to fight if they are true decorus and not hybrids such as sp. 5 "valentine."
Do not raise the temp too much, I lost all six of my synos (plus my original Steatocranus "dad" and one Synodontis nigriventris) after raising to 30C, stick to 27C maximum with masses of water surface rippling.
I used Sainsburys Course Sea Salt, 0.25g/l on day1 and another 0.25g/l on day2, alongside Protozin to cure the other fish that did not die. If I did not have salt ensitive fish in there (an Aboricthys elongatus), I would have doubled those salt doses. I gave the fish basic food rations (1 small portion a day) while keeping the same water (with meds added) for 13 days, then did a 50% water change (with no salt) on days 14 and 15.
* Synodontis decorus are normally very social synos, having a goup of 6+ is positively recommended, but like Clown Loaches these catfish get big/active and need a 6x2x2 minimum for life. They grow quite quickly, my six went from tiny 3cm babies to 10-12cm SL (with ~2cm diameter bodies) in ~8 months, when I guttingly lost the whole group.