Sorority initiates left to clean house over Spring Break inadvertently release a blood-thirsty, body hopping demon. With the dubious assistance of a senile groundskeeper and a couple web-cam wielding perverts, the co-eds must defeat the demon before it gains enough power to escape the house.

I think this is a bit long. I'm assuming its a Horror/Comedy and you are trying to communicate that here.
Throw out dubious, pick either the senile groundskeeper or the web cam wielding perverts and say something along the lines of "with the assistance of kooky characters such as a senile groundskeeper" Basically highlight one and generalize the other.

Play on the irony of the sorority initiates being stuck in the house and it will sound awesome to me! :D