These books are so weird. I'm really thinking they are horror books. 

"Don't you love me?" "Yes! We love you in soup!"

I don't want to post spoilers, but if you've read the series, this reddit expresses all my thoughts. 

https://www.reddit.com/r/books/comments/stetme/i_forgot_how_creepy_the_original_wizard_of_oz_was/