I think there's something to be said for having two of the same genus, if not the exact same species (like having two different types of Zons, like you're considering). We weren't sure what to expect in terms of a reaction when we brought our second Zon home, but they've worked out a "flockmate" relationship. They'll occasionally bicker or squabble, but mostly just posture at each other. They're capable of hurting each other badly, and they never have (we of course watch carefully). This could all change at puberty, and we'll be watching for that. But for now, they do fine, and it's been fun to watch them teach each other everything they know how to say. Interestingly, the one very powerful bird bond that has formed has been between our cockatiel and the OWA. It's very much unrequited love, too. The cockatiel MUST GO wherever the OWA goes, must sit on top of his cage or on the person who is holding him at all times, and occasionally they preen each other, but other than that, the OWA doesn't seem to pay attention to his presence at all.
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