All the Lovely Bad Ones by Mary Downing Hahn

Travis and his sister, Corey, can’t resist a good trick—so when they learn that their grandmother’s sleepy Vermont inn has a history of ghost sightings, they decide to do a little “haunting” of their own. Scaring the guests proves to be great fun, and before long, the inn is filled with tourists and ghost hunters eager for a glimpse of the supernatural. But Travis and Corey soon find out that they aren’t the only ghosts at Fox Hill Inn. Their
thoughtless games have awakened something dangerous, something that should have stayed asleep. Restless, spiteful spirits swarm the inn, while a dark and terrifying
presence stalks the halls and the old oak grove on the inn’s grounds. To lay the ghosts to rest, Travis and Corey must first discover the dark history of Fox Hill and the horrors
visited on its inhabitants years earlier.