They are caught up in something larger and yet they retain their free will...very, very nice.

The same magic of the castle fills this charming and elegant story.
The castle resembles an old, meddling and omniscient Dumbledore and just right for this reason with love it.
So it is no wonder that, as you write, the stone lingers in remembering the last adventure lived inside its walls, “reminding for this preference the partiality of many mothers with their youngest children”
You have a wonderful light touch in depicting scenes of normal life, the develop of a relationship, the enchantment that entraps who live there, the excitement of the waiting for the students who are the very lymph of the castle.
The final brief scene between Severus and Hermione is cosy and sweet, full of hope for the future.

I especially like the way that the life-blood of the children in the castle is also the life-blood of the stone, and the creepy description of the crows changing their cries.

Lovely central image. Reminds me of an Israeli song (about the Western Wall of the Temple Mount): "Yesh anashim im lev shel even; Yesh avanim im lev adam - There can be men with hearts of stone; There can stones with human hearts." (It's better in Hebrew.) I particularly love your description of the castle's moving staircases: "It often relaxed his joints to change their position, and the movements seemed those of a stretching athlete."