This is from my fishie bible: "...can do very well if it was net collected (cyanide-affected specimins are, fortunately, becoming less common) and if kept in a system furnished with live rock, which affords constant grazing opportunities."
It goes on to say that they're not aggressive towards other fish, not reef safe, it does best on a combo of frozen foods containing spirulina algae, mysid shrimp and/or finely shaved fresh or frozen shrimp, but min. tank space should be 55 gallons.
On the lemon peel and flame, both only require a min. tank size of 20 but they're said to be aggressive to other members of the same genus. Plus it says the lemon peel is not known to be very hardy. Just judging from this book I wouldn't recommend putting the two together.
Of angels those listed as being less aggressive towards other angels than some, not *terribly* hard to keep, and ok for your size aquarium are: coral beauty, eibl's angel, and fisher's angel. It sounds like it'll be kinda tough to find two that will fit in your tank and possibly not fight. Why not go with a flame and something else?