From your posts I am assuming that the plucking started after the death of your sister, and he is probably reacting to that, he misses her, and she lavished a lot of attention on him. He needs more time out of the cage and more attention to help him stop this cycle of plucking. Greys do require a certain amount of daily attention, you cannot stick them in a cage and expect all to be well with them.
Usually when they go thru a molt, they lose more feathers than usual but not all of them at once, like Dan stated, they have to be able to fly if they were in their natural habitat.
Try these suggestions and see what happens, but whatever does it will take time and patience, this will be a slow and gradual process.
Be sure to keep us updated as to how it goes with Kenworth.