They potentially should be able to co-exist in the same tank, but I'm afraid that's gonna be too much fish and too much
bio-load for a 55 gallon.
The yellow tang can reach up to 7 - 8 inches (~20 cm)
The Lionfish can get up to 12 inches (~30 cm) - a very messy tank member, needs
The Snowflake Moray Eel can get up to 24 inches (~60cm) - also a very messy member, needs bigger than a 55 gallon
If you get all these fish, you'll end up having algae problems out the wazoo because of the high levels of nutrients in an overstocked tank.
Then only one I think you could realistically get away with putting in your 55 is the yellow tang. When it matures though, I think a 55 gallon would cramp it. Tangs need lots of swimming room.
What about the dwarf angels? Have you looked into those? You'd only be able to get one because they'd prolly fight in multiples in a 55, but they sure are purrrty!
http://www.fishlore.com/profiles_cor..._angelfish.htm