As far as bonding pairs, with fish like angels it just a matter of the luck of the draw. If you can't definitively sex them and you get 2 males, they will likely never bond, and may actually become more aggressive towards each other as they mature. They are not like wrasses and clowns where they change sexes giving way to the more dominant. Angels are born either male or female and stay the same. This goes for many fish, when you get lucky and get a male/female pair of species you can definitively sex, it works; if you get 2 males you usually end up in trouble.