JKR deliberadamente manteve a família de Hermione como pano de fundo, já que eles não eram muito interessantes para a história.
Does Hermione have any brothers or sisters?
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.
– from interview with J K Rowling at the Edinburgh Book Festival, 2004-09
Como tal, faz sentido não lhes dar nomes além do seu sobrenome, uma vez que não foi considerado um detalhe importante.