I would guess given the shape of the mountains and of Sandman, Davy wants to claim both hills because one or both is home to a Wight. The Wight is just a macguffin for his plot; it has unspoken levels of power and is very valuable but it's not crucial. That said we do have too many simultaneous villains; I count three major antagonists (Angel conflict, Davy, Cultists) with a handful of infighting at each stop, plus the Shadow Spirit which could be the Cultist goal? Making the Wight be the thing that ties them together at least eases the knot.
I would guess the school is ultimately not important except for as a subsection of the Davy plot, and the Activity Consortium are generally on the side of the Activity Club, with Penny and Isabel's father not being additional antagonists but supporting characters. Notably, Penny allows for BL to "die" without throwing things into disarray, or at least gives Zack some breathing room vis a vis handling the Wights.
I'm using Clayview as a nickname for the "Burger" Wight, and without further information I am assuming it's distinct from both the Angel and/or whatever Davy is after.
We'll know more details by Friday evening though, sooooo