Tevye can be stubborn, submissive, and a bit antagonistic. He will also poop on you much more than George will (and his poops are often very wet). George is dominant and has seasonal aggression, in the spring. He sometimes bites (hard) and can be territorial over his cage, sometimes with food. It can be good to keep them in separate cages during aggressive phases, with separate food bowls. It is helpful to keep them partially clipped - especially George - as it curbs a lot of his aggression. Both are very codependent and do not tolerate being apart well - if they are not visible to each other, they will scream. They are very brave around other animals. Tevye has has been known to land directly on a cat's back several times (antagonistic behavior). They have not been trained much to tolerate hand-training (like gripping them/grabbing them) though they tend to be quite docile when they are handled by the vet or bird groomers when getting their wings clipped.
Separation anxiety/being out of sight of their brother. Less phobias, but things they don't like include hats, gloves, and unidentifiable things close to them (but these are likely able to be overcome with some work - not phobias, mostly lack of exposure).