In a 75 gal tank, if you want to you can keep harem of dwarf angels. I keep harem of 3 Flameback angels (a thread somewhere) and, not at the same time, pair of Flame Angels in the past.
You want to introduce at most 1 male in small tank like this. Two males will/likely will fight.
All dwarf angels are protogynous hermaphodites, so you will end up with one male over time. This is a bidirectional changes so if you accidentally introduced two male, world war will happened and the looser will reverted back to female if he survive until the change.
All Dwarf angels are dimorphic so if you research into it, you can get information about this for the specific species, however if you get smaller ones, they will be most likely females. Flameback and Flame angels dimorphic characteristics are well know (to me) and easy to see with just a glance at the fish. I don’t keep Coral beauties so I don’t know, so cannot help you regarding this species.
I like to keep harem of same species but to each his own.