Ruby & Olivia / Rachel Hawkins.

Enhanced descriptions from Syndetics:

Ruby is best friends with Emma, but she and Emma's twin sister Olivia are definitely not friends. Unfortunately, Emma will be away for the summer, while Ruby and Olivia are going to be stuck at a community service day camp for troublemakers-together.

To kick off the spirit of service, the campers are outfitted with bright pink polka-dotted t-shirts with smiley faces on the front, then tasked with cataloging the contents of an abandoned mansion. Sorting through objects in an old house sounds boring, and working with each other is that last thing the girls want to do, but the stuff is actually pretty cool. There's everything from mink stoles to golf clubs to stuffed deer heads . . . and . . . wait . . . is that stuffed deer head watching them?

When the taps run freezing cold and doors slam inexplicably, Ruby and Olivia wonder if the other campers are having a bit of fun, or if the abandoned mansion is looking for new residents. To solve the mystery, Ruby and Olivia will have to put their grudges aside and figure out how to be a team with or without Emma.