Hi! Here's the line up and my comments on each (I would suggest only two fish max...that's what I did with my ten gallon reef, it worked out very well):
flame hawk: I'd avoid this one. He can sometimes eat ornimental shrimp, and likes to "perch" on corals...in such a small tank he could cause some real problems by irritating corals and not allowing them to open up and feed.
percula clown: Great idea. I had a pair in the ten gallon, worked out just fine. One alone would be cool too, then you coould get another fish to go with it.
yellow-headed jawfish: Could work, but they like to dig around...in a small tank like a ten gallon it could get irritating. An idea.
firefish: Nadda. Cool fish, prefect for a smaller tank, but it likes to jump.
royal gramma: Excellent fish.
pseudochromis: Don't these need to be in schools? Not sure. Jury's out on this one.
My suggestions: one
royal gramma and one percula clown.
HTH,
Raszagil