Hallway test.

Stranger count: 3 male, 5 female

Set one:blue boy and "Speedy" the little sable merle - Speedy was head up tail up trotting around the hallway and the living room. Not problem. Blue worried.
Set two: Sable girls - sable girl worried, easily lost. Sable merle girl quicker and tail up
Set three:Blue girl, white nose tri (notch collar). Tri better, both easily lost
Set four: Bob and the shawl collar tri - fast, followed mom down the hallway, a little vocalization once in the living room. Bob tried to get on the couch. Didn't work.

They really don't react to the other dogs - just toddle right past them, and only seem to recognize mom. They have reached through the xpen trying to touch the other dogs, and rooted around in Brick's fur the times they've encountered him, but it is much like they'd react to an inanimate object. They definitely know mom and not mom.