I can't tell anything from those pics I'm afraid.
Are there treatments / producers I can carry out shot term with a sample of the water from the tank in a small suitable container with just a heater for a short time?
I'm in the same boat with lack of space for extra tanks, so what i do for quarantine is put the fish in one of these:
Mine is 30L in size and food safe (wine glass and fork symbol on it). Cost about a £5er. It will hold the water fine, but I don't suggest you move it while full! (Note - I checked mine by filling it in the garden first - just in case!!)
I use a small internal filter with some cycled media and a little heater. I have some cheap decorations from Pets at Home in there to give them some hiding places.
Then for quarantine I do a week or so of settling in and getting them to eat.
Next I do a course of Discus Fluke Solve (praziquantel) for flukes and some common types of worms.
After that I do a full water change (2 x 50%) then a course of Seachem Cupramine. This eliminates velvet, ich and something else I've forgotten.
It takes about 5 weeks in total for all of that.
If I see other illnesses during that time, I will look up the symptoms and treat as needed, but all my fish go through the above whether or not they show symptoms. as those diseases are just so rife in the hobby.
PITA TBH but needs must. When finished don't put the media back in the main tank in case the copper etc leaches out of it.