Jude Ellison S. Doyle 
Neighbors, The #2 [PDF ebook] 

Casey’s uncanny behavior and obsessive interest in her younger sister raises suspicion in Oliver as he spirals into further paranoia that his step-daughter and their neighbors aren’t who or what they claim to be. Oliver’s fear becomes so overwhelming, in fact, that Janet’s family must fight to keep themselves sane, as the outside world becomes increasingly monstrous