One decent start deserves another. I brought Anna down again to her tunnel. Rhea hung around for a while but seemed more likely to just hang around the borders.
When I gave her and Davout and Anna some treats she soon came over to peer in the front gate. Conflict of personalities or does Rhea just want those treats? Hard to say.
After a little scuffle Rhea gave up and moved off, and I gave Anna a little break by partly covering the front with the blanket from the top.
With the cover and the tension down, Davout came close enough, say four feet, to peer under the edge of the blanket.
After a bit more than half an hour, I took Anna back up to her room. This time the kittens were less excited/agitated about it. Rhea ate the treats Anna left, Davout calmed down, and even Anna was pretty quick at recovery back in her room.
Perhaps the cats will tolerate each other just to keep me from messing with them all the time. Knock on wood.