Whats a good halloween costume group for 7 maybe 8 girls?

My friends and I (laura, carly, ana, eva, kerry, hanna, erica, and I) one of them may not be doing it so its 7-8, wanted to do a costume group for halloween. We're all in eighth grade and on the verge of being 14. We don't know what to be so any ideas are good! ten easy points! thanks(: