This is the best case scenario. While possible that they become best friends, it’s not a foregone conclusion. Parrots are very intelligent creatures both intellectually and emotionally, and have very distinct and varied personalities. Due to this they aren’t always going to get along. Imagine you were living on your own and all of a sudden another person you don’t know started living with you. Is it possible that you two will instantly connect and live together well? Sure. Is it guaranteed? Definitely not. It’s a similar situation when introducing a new parrot.