The thing is - I don't quite know it yet either, and I want to. I want to know that back story. I want to know their history.
Unfortunately, since it hasn't been written yet, I'm as much in the dark right now as readers will be later. But the author should know, right?
So I have two little side projects along with writing my main MS -- I'm going to write that back story. It will really just be for my own edification, and probably no one will ever read it, but I will have it, and I think it will help with writing the novels.
Because as they say--you don't really know where you're going unless you understand where you came from.
They will be short, maybe about 30k - 40k each, 2 novellas which chronicle the beginning.
Do you ever experience this when you're writing? Or do you usually already know the history of your characters and your story when you start?