1) The meatiest food possible. When I'm feeling lazy, I grab a cube of frozen mysis. When I feel like taking a little more time to feed my corals, I use a Food Mush which is different sea foods, vitamins, and fish foods all blended together and frozen.
2) Yes, it's possible. Rarely will a coral from the same species harm each other, and it's not too often that corals from the same genus but different species do any serious damage.