Are the two birds in the same cage, if so, please get a second cage and separate them. It is never recommended to house different species of birds in the same cage in your case the green-cheek could severely injure your budgie. Since you and your brother are already planning to get your own places I would not encourage the birds to form a bond, they are both young and if you work with the budgie and your brother with the green-cheek when you part ways then the birds will be bonded to you and your brother and not so much to one another.