In the original script for the bachelor party segment there were four vampires. Unfortunately the actress playing the part arrived on set and wasn't feeling well and had to leave before filming her part. As such several changes were made on set to accommodate the fact that there were now only three vampires and many of her lines were split up among the other three actresses playing the vampires or just taken out completely.
In the original script the main characters in the wraparound found themselves at the home of an older couple after their car broke down. Seth calls his sister to come get them and when she arrives she is revealed to be Maddie from the bachelor party segment.
The name of the cat creature "Bitsy" was named after the cat that screenwriter Todd Martin's wife, Trish Erickson-Martin, had when she was younger.
Screenwriter Todd Martin is a huge fan of the Spider-Man character Gwen Stacy and as such usually uses her name (or at least part of it) for his character's name. In this film the main female character's name in the "New House" segment is named Gwen and for the "Bitsy" segment Chelsea's last name is Stacy.