For those of you that don't know, this series is being co-authored. With more than one person working on a story, it can get a little crazy, as there are multiple visions and directions the stories can take.
Most of the time, the story writes itself as characters interact and it just unfolds.
Sometimes the characters get off track and we end up with pages upon pages of bonus material (Or whole new stories in some cases).
And sometimes we imagine the story going one way, and it ends up going another. Which isn't always a bad thing. Though it involves some rewriting.
The best part of writing with another person is keeping each other on task. If one person gets distracted by whatever's on TV, normally some kid show given the two children in the house, the other pulls them back on task. Unless the other gets pulled in too... then we're off task for a few minutes. (Hey, don't judge, some of those kids shows are designed to suck you in and they do their job well.) :)
It's also easier to write different personalities in characters when you have two different personalities writing separate people. The characters come to life and become part of your everyday discussions.
Some of the challenges are trying to decide what course of action the characters would take, and if those actions get the story to the point both authors agree is the heart of the plot. From time to time there are disagreements about what's important and what isn't. There's discussion about points that are or aren't important.
One author might want a scene drawn out where another might decide it's not needed. There's struggle over which is right and which direction the piece is heading.
But, even with these struggles, it's been an awesome experience writing a set of novels with a friend. Sure there's been some debates and raised voices as we work material out, but in the end... the characters lead the plot to the place it goes and the story told.