Try increasing the temp at which you are keeping the turtles and give them a very hot basking area. You can just use a 75 watt light bulb in a reflector lamp for the heat. If only mild respiratory problem the hot basking can dry it up. You might be keeping them to cold and thats why they are getting sick unless you keep them together and one was sick when you got it. Sounds like the map might need meds, I think Baytril is the name of an anit-biotic you can get from a vet. You should be able to ask the vet what to use and just buy it from them without having to pay for a visit. I would seperate them as well if they are together just in case.