No. They should be kept in groups of 6+. Preferrably with plants.
Sexing them is difficult. The general method is either splicing them open and checking out their reproductive organs, or by guessing at their size and whether or not they are fat with eggs or just full.
If 6 angels give you a chance of 95%+ at getting a pair, I'd say with six taht you should get at least one female and the rest males or one male and the rest females.