Dear Pete,
Please read my answer to your other post. YES! This will probably cause a MAJOR problem where both birds will be competing for you and your shoulders. Please read my "LIving with Merlin" articles in the article section of this site.
I misunderstood from the other post and misread that you worked at the bird store. Now I see that you are home for most of the day. I realize that Coco feels very close to you but suggest that you find some kind of alternative for Coco. It may be in another home where you can visit or something.
If you are concerned about company for Dukey, get something like a pair of parakeets or something. Get another bird that she will not feel competitive with. Basically, Dukey already sees you as the other member of your small flock, and since this has been for 6 years, she would probably be upset about any new bird that you bring into the house. It would be seen as an "outsider."
Again, if you have specific questions, contact me at merlin@AfricanGreys.com
Blessings,
Maggie-