Forgive me if I'm wrong, but I can't see a filter in there, or a heater. Water temperature as well as basking temperature should be at the recommended temperatures for the healthiest of turtles.
The screen cover's mesh should be at least 1/2 inch apart, so less UVB is filtered out (unless the holes are huge, UVB rays will be filtered out anyhow under a mesh cover). I only see one bulb there, so is it an MVB? Turtles require UVA and UVB to stay at their best, and unless it's an MVB bulb (which has both), you need two bulbs, a normal incandescent bulb will do for UVA, as it gives off heat and light, and a UVB to promote active turtles and shell growth.
If it is an MVB bulb, check the basking and water temperatures so they are normal, MVB bulbs emit a high amount of heat and is not recommended for smaller tanks (55 Gallon minimum recommended), and can overheat your turtle's habitat. If so, you can raise your lamp higher until it reaches the preferred range.
This is not as important as what I said above, but some turtles have been known to bite their glass thermometers (as well as glass heaters), so you might want to change your thermometer to something safer such as a digital thermometer, or a stick-on.
But other than that, your turtles look very healthy and happy,
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Hey hey hey.
so what do you guys think 
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