I've had two pairs in the past, both cacatuoides, one was the orange flash, the other triple red. It's extremely easy to tell the difference between males and females as they are completely different in coloration.
I would advise two females to one male and this is what I would get if I decided to keep them again.
**Edit**
My bad, I kept one pair of cacatuoides and a pair of agassizii, the agassizii were the triple red varient. And I would still go with a trio if possible.