I foresee failure.
First of all, 9 characters plus a kid, really you need so many? Why? Really WHY do you need so many? Have you ever thought about WHY you need so many?
How more characters you have how more work to make them tick, how more work to make the story tick and so on. True you can't have a murder mystery with 3 or 2 people including the dead guy/girl. But there is also having to many seemingly important characters.
There is a reason that slasher movies have so many teenagers, because they don't require that much work, many of these characters are just given quirks, not even a backstory, just a quirk, X smokes weed, Y sleeps around, Z is black, yes I know... that is how these movies go. They are given very little time to show off their quirk and the slasher begins to kill them off one by one.
The problem is NOBODY CARES about these people. It works in a slasher movie because, well comedy/horror, it isn't even scary. People know precisely what is going to happen.
But in a book? Characters need more then just quirks, they need backstories, personalities, reasons why they act certain ways. I see failure in your future.
But go ahead... try it! A book is not a movie. And having fun ways to kill of characters won't safe your writing project. Because, if nobody cares about a character, they also don't care if those characters die.
If you really want to write a slasher/horror story. First begin simpler, cut down in the number of important characters and do the backwork, give them all backstories, personalities and the likes and make sure that the reader actually FEELS with the characters. It is hard to feel for a character that is just a quirk, much easier for a character that is fully fleshed out!