Q. Does Hermione have any brothers or sisters?
JKR. No, she doesn’t. When I first made up Hermione I gave her a younger sister, but she was very hard to work in. The younger sister was not supposed to go to Hogwarts. She was supposed to remain a Muggle. It was a sideline that didn’t work very well and it did not have a big place in the story. I have deliberately kept Hermione’s family in the background. You see so much of Ron’s family so I thought that I would keep Hermione’s family, by contrast, quite ordinary. They are dentists, as you know. They are a bit bemused by their odd daughter but quite proud of her all the same.
(Q. Est-ce qu’Hermione a des frères et soeurs ?
JKR. Non. Au début, quand j’ai créé Hermione, je lui avais donné une petite sœur, mais c’était très difficile de la faire rentrer dans l’histoire…)
Désolé, mais pour moi cette déclaration est TRES explicite.