One of my very favorite things about your recent Snape-centric work is the way you're able to weave what we know about Snape from the last two books (especially) into your fic - and this was no exception. Wonderful family members who feel perfectly right, especially Cynthia, who acts just as I'd want to be able to act with Snape, if he were a member of my family.
And while I think that in the ::koff:: real world, it's probably unlikely that Snape and Harry wouldn't recognize each other, it's always seemed to me that non-recognition would be a key element in the genesis of any sort of believable relationship, since there's probably too much baggage for either of them to accept the things they do have in commmon. You do a lovely job of letting them learn about each other slowly and peacefully in this story. All in all, lovely work. Well done!