Thanks for the interest! The first one is probably a good place to start. Here is the link http://www.amazon.com/Preacher-Angry-Edenites-David-Rollins-ebook/dp/B00H5UMFY2
For the most part, The Child is a standalone story. However, there is a sort of epilogue where all four main characters meet up before the journey to Eden begins. The first four books in the series relate to how they all ended up in one particular convenience store at the same time.
I hope you enjoy it. It is a fun read.