The greys still do not physically interact at all, but I've recently realized that they are rarely more than a couple of feet away from each other. They basically ignore the rest of the birds, but are fascinated by what the other grey is doing. Stella seems to be the one who usually follows Max around, though it is occasionally the other way around.
Here they are, destroying the mail pile:
What would happen if we introduced another grey to the flock? There is the sweetest timneh ever at the rescue right now. My curiosity will have to go unsatisfied in this area as we are in a really good place and don't have the room for another bird right now!