This could be a viral issue, a bacterial issue or it may be parasitic. The selling of the eyes usually coes along for two reasons one is a Vitamin A issue and the other reason is a respiratory issue. With a respiratory issue you would notice bubbes fro the nose or mouth, gaping, wheezing or sneezing.
You do need to get a UVB light on these turtles. Without a UVB light and a calcium supplement they are predisposed to Metabolic Bone Disease. The UVB and calcium also helps with the immune system. With out the UVB the immune system is compromised. This is soe information on UVB and Metabolic Bone Disease:
The swelling in the eyes can be from lack of circulation and accurate humidity. Vitamin A deficiency can cause this problem and can also lead to secondary eye infections: http://animals.mom.me/eye-problems-turtles-2214.html
I never suggest a fish tank for turtles or tortoises. There is not enough air circulation and can lead to respiratory issues as well as other problems. I suggest a tortoise table for them. you can see that here:
http://www.reptilesmagazine.com/Turtles-Tortoises/Tortoise-Care/Indoor-Tortoise-Table-Housing-Pen/ This is just an idea about some turtle enclosures. I am also going to give you a care sheet to help with the husbandry: http://turtlepuddle.org/american/boxcare.html I recommend a Reptisun 10.0 linear tube to go over the enclosure. It should not be any more than 12 inches from the turtles.
To help them lest start with some Sterile Saline eye drops 2 times a day in each eye. I would also like to see you give each turtle a soak in a 50/50 Pedialyte soak for 20 mins. This is a theraputic soak to help hydrate them with electrolytes. I would like to see you using some plain calcium powder on their food and keep cuttle bones available for chewing as a calcium supplement. I think if you get the UVB bulb over them it will help with the lethargy. Until you can build some type of tortoise table you may want to switch them into a large Rubber made tub which some people use.
I do suggest a Herp Vet visit and if you supply a Location I can try and find some Herp Vets for you. I also suggest some Natural sunlight for 15 mins several times a day until a UVB light is in place. Natural UVB from the sun will help with the immune system.