When you start a game in Book 2, it'll ask if you have an existing save file. It's looking for a file called Act6.sav (the final save of Book 1); if it finds that, it'll use it, otherwise it starts a new fresh game.Are you going to be releasing book 3 any time soon on Steam?
When you do release book 3, am I going to be able to use my save from the developmental path of book 2? I ask because I wasn't able to import my book 1 developmental path save into book 2.
Book 3 works the same; once you start it'll look for act11.sav2 (the final save of book 2), and import that.
Apart from that, you can play Book 3 on Book 2's development branch.