Awesome, Bubblybutterfly178! I would absolutely love to help you out with your story!
The first girl who is a friend: Jessica, 12 years old. She has blond hair and light skin complexion. Jessica also helps Scarlett along and always consoles her and helps her when Scarlett needs help.
The second girl who turns out to be bad at the end and who is a creature: Mae, and her age is around 13. You think she's a really cool friend - like Jessica, almost - but then she ends up betraying you, or becoming a bad guy.
The third, the boy who is also a friend: Jacob, also 13 years old. He is a very helpful boy, and, like Jessica, helps Scarlett out when needed. He has darkish (like around light brown) skin complexion.
If you need any more help with your story, please let me know. Don't forget a title for your story!
I hope you have fun with your story!