Turtles are also absolute poop/ammonia factories. Keeping fish with them calls for a lot of attention to water quality if the fish are to have any kind of healthy life.
Expecting fish to "clean up" after turtles is pretty much a pipe dream. The fish may nibble at scraps of food that the turtles miss, or which they create when tearing an item apart, but generally speaking the clean-up crew is you. Your tank will stay much cleaner, much longer if you take the turtles out and place them into a small container with a few inches of water at the correct temperature for feeding purposes. Leave them there long enough after the meal for them to have that big post-meal dump they tend to have before returning them to the aquarium. Everyone...the turtles, any potential fish, and you...will be happier for it.
I currently have only one small aquatic turtle, a Stinkpot Musk that I've had for a few years, often living with fish. In the past I kept many larger aquatic turtles; with the exception of Softshells, I have never purposely introduced food for the turtles into their living quarters. Softies are not fond of handling, so they were fed in their tanks, and the difference in the speed at which water quality deteriorated was startling.