The Skelton Sisters are a pop duo in The Secret Series, made up of twin sisters Romi Skelton and Montana Skelton. They are part of the Midnight Sun, and even though the Midnight Sun is portrayed as devious and evil, they serve as the main source of comic relief throughout the books, being quite dim-witted, and both are dipicted as bimbos (an attractive but dim-witted woman who relies on her looks than her education and knowledge). Like real celebrity stars today, they are considered teen idols, because so many teens and tweens, and even children idolize them, including Amber and Veronica.

It is revealed even the narrator of the series cannot tell them apart, since they look so much alike. It is found out they lip-sync in If You're Reading This, It's Too Late, thanks to Yo-Yoji. Even though they lip-sync, it is found out they are still popular in You Have To Stop This.