I wouldn't attempt more than one dwarf angel in a small tank due to aggression issues. Since this is a FOWLR setup, that is really the only thing you would have to worry about in them beating on each other. It was covered above that it depends on the personality of the individual fish, but even this can change over time if you got lucky enough to have 2 mellow enough to live together...as you can pull out of melosu's post.