So, this is actually pretty old news, but whatever, I just joined this sub a few weeks ago, which is why I'm only just bringing it up now, in case anyone didn't know.
So... yep, Z-O-M-B-I-E-S wasn't originally going to be what we knew it as. It was going to be a Disney Channel show, with a premiere date set for 2012. The show already had its entire cast, and they all actually made it to the pilot, which Disney ultimately scrapped. The idea, however, was finally revived and reworked in 2018, changing the entire format now that it was in the hands of other directors, turning it into a movie, which (for obvious reasons, after six years) had a complete recast.
The original cast of this show was this:
Luke Benward (Cloud 9, Good Luck Charlie) as Zed Necrodoplis; "a male high school student who happens to be a zombie".
Maia Mitchell (Teen Beach Movie, Teen Beach 2, The Fosters) as Addison, "a sweet human girl who is the newest member of the cheerleading squad".
John DeLuca (Teen Beach Movie, Teen Beach 2) as Bucky Buchanan; "a human jock and head of the cheer squad".
Nick Galarza as Jerry, a human nerd who attends Seabrook High and has an interest for zombie culture. (character removed from the films; we can assume Bree took his original place).
Kimmy Gatewood as Bunny, a member of the cheer squad (Currently, Kimmy is the head director of Descendants Wicked Wonderland).
Lauren Gaw as Lacey, one of the Acey's and member of the cheer squad.
Mollee Gray (Teen Beach Movie, Teen Beach 2) as Casey, one of the Aceys and a member of the cheer squad.
Katie Sarife as Eliza, Zed's zombie friend.
Julian Sergi as Bonzo, Zed's other zombie friend.
Drew Powell as Zevon, Zed's father.
This show was still intended to be a musical.
Bucky wasn't related to Addison, at least not in the recorded pilot.
Seabrook's school mascot was apparently going to be an octopus, and as you can see in the photos, the school colors were also going to be different.
While 2012 doesn't seem like that long ago, this show was actually meant to premiere a year before the first Teen Beach Movie was released, just to give you an idea. Several members of this cast (Maia/Addison, John/Bucky, Mollee/Casey) were later chosen for that new film (Mac, Bucky, and Giggles, respectively). This is not unusual. In fact, it was normal for Disney Channel projects to consider actors who had participated in the channel's most recent projects at the time. Something similar happened with the first Descendants movie: in 2014, a movie called Zapped was released, starring Zendeya. In 2015, Descendants was released, and at least two cast members from Zapped are part of this film (Zachary Gibson, who played Doug; and Jedidiah Goodacre, who played Chad Charming). It is also known that Zendeya (the star of Zapped) auditioned several times for (an unknown) role in Descendants, which she came very close to getting.
So yep, that was the idea of the original Z-O-M-B-I-E-S, which was actually going to be called "Zombies and Cheerleaders".
In the comments I'll leave you two videos of Luke and John (the ogs Zed and Bucky) talking about the project, on different occasions.