Fight? I'm sure you meant "keep as a pet". And obviously the microlions. I'd feed them ground beef and try to maintain a breeding population, eventually sell them as pets.
Could an ant sized lion actually hurt you? Their teeth are built to wrap around and grip thinner pieces of the body. If they are shrunk down, I don't know how efficiently they could work their way through skin. It'd be like trying to bite a wall or something.
Don't know about that, but think how strong ants arenin proportion to their weight. If that carried through, it could probably just batter you with its legs/head.