There are lots of threads regarding mixing dwarf angels. A general rule is that it's not a good idea, unless the tank is very large, and the fish ae introduced siumultaneously. If you have one dwarf angel that is behaving, adding another may upset the apple cart. If you end up having to remove one, you'll likely have to dismantle your tank. Very difficult fish to capture.
Reef safe means that they won't harm your reef inhabitants, specifically coral and other inverts. It's always a crap shoot with dwarf angels.