Grey togetherness

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:

I think Max was looking for a little alone time, by perching on the seat of a chair that was pushed in to the table, but she discounted Stella's detective skills:

I thought perhaps they'd both sit on the chair, but Max took off as Stella arrived, and then Stella followed Max to the stand:

This morning, on my newly washed counter:

They've even taken to both being on the same stand.  Before, this was Max's stand and Stella stayed on the green stand:

They are so interesting to watch.  I wish I knew what they were thinking.  Do they keep such close tabs on each other because they like each other (and, if so, why don't they allopreen?)  Or do they not like each other and have to make sure that the other one doesn't get preferential treatment?  Or am I ascribing human feelings to them and they're just doing it because of the flock mentality that's hard-wired in their brains?

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!