Most avian vets will do the dna testing. And also some bird stores will do it I know where i got my macaw from they would. And some places allow you to collect the blood yourself and send it in but I just dont feel comfortable doing it myself yet.
It should work but there isnt a guarantee. You couldn't just put them in together immediately you would have to let them get to know each other. But all should be fine since they are flock animals just keep an eye on them and like said have two seperate nest boxes.