Urban Fantasy series' discussion

Where are the sisters? Why is Frozen the exception?

Just wondering, are there any fantasy / action adventure / science fiction stories about two sisters? The two brothers theme is ubiquitous. Supernatural, Vampire Diaries (even the spinoff is about the two original brothers; they only have one sister), Cal and Nikko, Thor and Loki. Even Harry Dresden eventually finds out he has a brother.

There are some brother sister combos like Max/Isabel in Roswell. Buffy has Dawn but does that really even count? There are several examples in books I’ve read of male/female twins, but I’m really having a hard time of thinking of sisters. Most of the ‘heroes’ are only children male or female but when siblings are central to the story it is usually brothers. Frozen is a recent exception.

Running through my list of favorite female heroines, I can think of a few with a sister as a minor character but not one where the relationship is central to the story.

Can anyone give me some examples?

There is actually another Snow White fairy tale where she has a little sister named Rose Red. They are actually quite close in it. Fables the comic book includes her, and I was quite happy. I suggest looking it up since it's pretty much what I thought Once Upon a Time was going to be like, but then wasn't. It's an ensemble cast though, so their relationship isn't central, but it's well done.

So, I am not sure how completely "central" to the plots all of the following relationships are because let's face it most of the main characters in UF and fantasy books are basically orphans but here goes nothing...

In Fantasy books:
*Sansa and Aria Stark from 'A Song of Ice and Fire' (Game of Thrones) books by George R. R. Martin
*Viviane, Morgause, and Igraine from 'The Mists of Avalon' by Marion Zimmer Bradley

In UF books:
*Eugenie Markham and Jasmine from the 'Dark Swan' Series by Richelle Mead

Here is a Urban Fantasy series I can think of but haven't read yet:
*Witchling (Sisters of the Moon, Book 1) by Yasmine Galenorn

Sadly, that's all I can think of for sister stories; as for brother and sister stories there are a few more like 'A Song of Ice and Fire', 'The Mists of Avalon', 'Black Dagger Brotherhood', 'Sookie Stackhouse Series'...