You shoulda let them keep thinking, "I know that guy from somewhere....." and gotten on with a bit of a convo if you could. Would have been interesting to see the wheels spinning in their mind as you brought up some things.
Had I not known either of them I would have simply listened and let the conversation go from there. But it was only four years, and despite the beard, I had to assume the one sister recognized me. It was strange that she didn't acknowledge me when I opened the door. Maybe she was shocked or maybe it was a weird japanese cultural thing or dementia or ...