I know you are probably sick of hearing from me, but there is NO way to know if 2 birds of different species will get along....and a size difference means even more complications.
Even if you get 2 of the same species, there is NO way of knowing...(and even 2 that are the same size can get very violent, in theory).
Much like people, they are individuals, and a lot changes when they grow up...So 2 babies could be find, but give it a few years and you may be dealing with a very complicated situation.