I only recall one Grandparent, my old Nan, I cannot recall ever reading with her, however, to my shame I do recall spoiling her reading! Old Nan used to take a chair out in the garden, spend ages putting it in the best position and settle down to read her book, I would creep upstairs and sprinkle water down on her, she would think it was raining and come back inside, this I did for years and she never twigged.
It didn't stop there though! I used to creep in her room and she always had a book on her bedside table, I would move the bookmark back several chapters and sit poker faced as she complained that "another book has printing errors, repeating chapters that I have already read!"
so I have memories of books and Grandparents, but not probably what you were looking for!
I am now a Grandparent a have a stack of books waiting to read with our Grandson, I can't wait!