You may house fishes and red-eared sliders together. Malayan box turtles aren’t suitable to be housed with fishes as they are poor swimmers and require shallow water levels.
Here are some factors to note when housing fish and terrapins together.
Tank size: your tank has to be large enough to accommodate all the fishes and terrapins.
Filter strength: the filter has to be strong enough to clean out the additional debris contributed by the fishes.
Fish breed: avoid small and aggressive breeds. The ideal breed to house with terrapins would be tetra fishes.