I would get them feeding on pellets. I prefer Hikari sinking carnivourous pellets. Also mine eats shrimp pellets and loves worms. Night crawlers or red worms. Dont be worried if they dont eat right away. Mine took some time.
Also, dont get knifes eating on one thing. They can be a pain to switch over if they get the taste of only certain foods. Good luck with them and post some pics!