The only solution to your problem is for you to keep the birds in separate cages. When you house two birds together, they will bond – even if they are the same sex – and once they bond, they become difficult or impossible to handle. This stems from their instinct – in the wild, adult birds do not have friends, they have a mate. Even if they live in a flock, they don’t interact with other flock mates socially – they stick with their mate and if another bird gets too close they get aggressive which is what you are experiencing. And the longer that Blu lives in the cage with the other bird, the stronger the bond will become and he will get to the point that you can’t handle him at all – even away from the cage. I know this is not what you want to hear, but if you want them to live in the same cage, you need to accept that they will probably not remain tame as pets.
Thank you for asking Lafeber,