The Long Shadows of October by Kristopher Triana
When Joe and Danny take on the job of housesitting Snowden Manor, they fail to realize they won't be in the house alone. Inside the walls swarms a specter made of equal parts ghost, succubus and witch, and she uses the manse as a prison for souls. Now that October's supermoon is falling over the mountains, she is ready to rise and reclaim her flesh.
Kayla has a crush on Joe, so when he asks her to come to a party at the manor she accepts his invitation. But no sooner do they get there than strange things start to unfold. People go missing, a mysterious dog appears, and then the boys begin to change . . .
Wraiths warn Kayla to save her friends before they're devoured by the seductive witch. But she must hurry. For as Halloween approaches, the manor becomes a vessel for the black magic of the mountains, and the shadows that rule the woods return home.