Author's Note: I've never had to do so much last minute work! (those yellow spots on their skin in the contest view is a lot clearer in the bigger version!)
These are the three gorgon sisters. While Medusa is the most famous one, she had two sisters, according to some myths. There is Stheno and there is Euryale. I also went for the stories in which the gorgons were pretty, and not very monsterlike.
Here is a closer crop of the three Gorgons, in case you want to see that.