Strays by Joe Rigney
Rodney, abandoned by his mother at his weird uncle Ray's, encounters a demon named Birthless and must figure out his uncle's secret while preserving himself, his newfound friends, and a sleepy Alabama town from destruction.
Strays is an unusual YA adventure story that's part C.S. Lewis's Screwtape Letters and part Tom Sawyer. The focus of the book isn't on simple lessons but is instead the story of a lonely boy realizing that there is more to the heavens than stars, more to books than facts, and more to his Uncle Ray than tie-dye shirts and honeybees.