Wicked: The Life and Times of the Wicked Witch of the West
by Gregory Maguire
Sarima's sisters never get names: they are either referred to as numbers (in the order of their respective births) or collectively. Even Sarima doesn't bother with their names, which may help to further fuel their resentment of the older widowed sister who is now keeping them from getting married themselves (thanks so some archaic customs).
These sisters rarely demonstrate independent qualities, and when they do, they often embody a Characteristic with a capital C. We have the bossier older sister, the spoiled younger sister, etc.
The sisters provide a lot of comic relief in the book as well as commentary on gender issues in Oz, where women didn't have a ton of options outside of marriage (or serving their older princess sisters, apparently). On the whole, though, they act more like bit players or extras in a movie rather than distinctive characters in their own right.