You should be able to keep those three lions together with little trouble. Just keep "size differential" in mind when choosing specimens.
The only two lionfish species you can sex with any degree of certainty are
D. brachypterus (fuzzy dwarf) and
D. barberi (green/Hawai'ian lionfish).
The
radiata will be the touchiest of the three species you've mentioned, as they often show up in rough condition (they aren't great shippers), and altho our specimen is a real chow hound, they are reportedly a bit slow to take to the stick. I do, however, feel that this may be due to them needing some "conditioning time" to get over their shipping "shock".
The
mombasaae is pretty easy and a gorgeous fish IME, but they can sometimes be affected by poor water quality (they large eyes may go cloudy).
Fuzzies are about as bulletproof as lions come. Easily weaned, and very spunky fish, and they come in many color morphs (brown, red, yellow, or any combo thereof). Assuming all fish are of similar size, add the fuzzy last.
I would however, wean each fish before adding it to the DT. If you can't have a QT for weaning, you can use Frank Marini's "weaning basket" technique (as described in Figure 17 of his
Lionfish Care Article ).
HTH