Spice girls

Part 2- Together as a gang or not?

All the girls go to the same school but are all in different classes (Hannah: class 4, Sophie: class 5, Summer: class 6, Stacey: class 7).
How the girls met:
Hannah + Summer = best friends,
Stacey + Sophie = best friends,
Hannah + Sophie = cousins.

They each introduced each other on the play ground one day consequently the girls got together and became BFFS (best friends forever).

After a few weeks of knowing each other, the girls decided to be in a gang. They did not have a name for it though.
One of the girls who go to their school in class 5 (Masie) sent out an invitation, which was I for all of them to share, for them to go to her halloween party.
The invitation said:

Dear: Stacey, Sophie, Summer and Hannah,
You are invited to: Masie's halloween party
At: 7 Church Hill Lane
Time: 6 pm until 7:30 pm
From: Masie Berry
P.S don't forget to dress up halloweeny
BOO!!

The girls rushed to show their mums - hoping they would say yes.
Their mums said yes.

The only problem is now
What to go as? ...