I ussed to buy goldfish and minnows for my turtle when it was still alive. fresh food like that will accually help them live longer. had my painted turtle for 15 years which I hear is almost unheard of.
Not to point out the obvious, but turtles should have WAAAY more room then just 10 gallons. That's kind of cruel. Especially putting fish in with them. Do your turtles have a heat light and places to get out of the water?? Hopefully if you get a bigger tank for your b-day you can put your turtles in there. The oscar needs much more room too. Im sure this has been pointed out and you've probably answered. But, you really need to do something about the turtles.