You're dealing with a few things here, the first of which is interspecies aggression. While it's no guarantee they will or won't get along, I personally know our younger caique Jack generally tolerates our other fids. I also know, however, that caiques are one of the more defensive species in terms of territory and because a bird gets along with other birds when young doesn't guarantee that in the future. I can also tell you that when a caique wants to bite, they bite hard and they don't let go easy. I'd rather take a chomp from my U2 than my caique. I would recommend two cages close to one another, and determine how they will get along as they age. They might socialize on top of the cages and then you can move them closer. If, as they age, they don't work so well together you can always separate the cages.