I don't know how to help with the aggression issues. I've been very lucky. My birds don't like each other but the respect each others space and don't go looking to cause trouble. Thank god!! I think the desensitization will help. Kili's been used to being the only bird. It'll take a while... hopefully you'll start seeing results soon!
On the quarantine issues you say "Needless to say, quarantine has been violated multiple times already. Truman has landed on Kili's stuff and Kili has landed on Truman's stuff. Living in a single room with flighted parrots makes a successful quarantine nearly impossible. I have been weighing the birds regularly and both seem to be doing just fine. Kili has been healthy for two years and Truman got a full array of blood tests by the breeder's vet. I am not having a strict quarantine anymore but I am keeping the cages apart and only taking one parrot out at a time until this aggression issue is dealt with better."
A true quarantine is almost IMPOSSIBLE to do. A lot of illnesses are airborne so to do a true quarantine the bird needs to be in a room where they don't share an air space. In modern homes with a central air conditioning/heating.. it's very hard to shut off a specific bird off in another room.
Here are some resources for that:
http://www.parrothouse.com/quarantine.htmlhttp://www.parrotparrot.com/library/quarantine.htmI make sure to take every bird that comes through my door to the vet. I don't take my birds to pet stores. But a true quarantine is SO very hard to do- normally, I separate the new bird in another room. And make sure to leave my "socks" at the door when I leave. I always wash my hands in between touching the new bird. That being said I'm totally contradicting everything I just said to say that I'm not doing a QT with Capri. The double macaw cage does NOT fit through the doorway. My breeder only breeds Capes and the Bronze Wing Pionus. She's had her breeding pairs for years. I know several people who have gotten birds from her. I know I'm still taking a risk still but I have confidence in her.
Anyway- I'm rambling... I hope Kili stops attacking Truman!