I have 2 diamondback female turtles with some community fish, guppies, barbs, sharks, loaches, and tetra's. Generally they do not go after the sharks, loaches, or catfish. I have been keeping them together for a year now and they have not killed or eaten any of the loaches, sharks, or catfish, but go after mainly the guppies and tetras. Usually its the brighter colored guppies and tetras that get taken out.
Every turtle is different and I have seen turtles that will eat any fish put into an aquarium.
Be prepared for a VERY messy disorganized tank. Turtles are VERY strong and will move everything you put in there. I have some pretty large rocks and they can still move them. I also feed them in tubs out of the aquarium with the aquarium water. This means more water changes because of taking so much water out but with turtles this is very necessary because they are so messy.