I had a pair in a 36x18x12 thats about the smallest I would keep mine in because Like I said I like mine to have plenty of room. But this is a personal preference. I now keep Mine outside in an aviary with on octagonal shaped flight with a 6x4 foot shed which is insulated and water proofed, and also heated.
But mine are spoiled.
I would not recommend trio's because they will fight. I had 2 females in with a male and the one female nearly killed her when she wanted to nest. I do mean she almost killed her she was torn to shreads. I managed to save her but barely. If you want expert advice I can give a link to a bird forum that I am a member of that will help you with anything you want. Send me a pm with your email and I will email it because I do not think we can post other links here.