a good brand of flake should be fine for those kinds of fish. I use tetra pro, and my fish love them. For bettas, freeze dried (or frozen) are a good treat but for a staple hikari betta-bio gold pellets are great!
also, as dan said, bloodworm is a good treat for fish. So you can use a good flake then once a week or so, throw in some frozen bloodworm for them
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for the khulis, at night take a pinch of flake and hold it under water so it sinks, the khulis will go straight after it.