When Apple released iOS 7, they added the ability to AirDrop files between iPads.
You can use this functionality to transfer your books between iPads.
1. Make sure both iPads have AirDrop turned on.
It's quicker just to make AirDrop available to everyone and turn it off when you're done. Slide up the panel from the bottom of your iPad and enable AirDrop.
2. Choose your book and export it
Go to the 'My Books' screen and tap the export icon. Choose a format (it should be ePub if you want to send it to Book Creator).
If the other iPad has AirDrop turned on, you can tap on their name to start sending the book.
Note: you can also access the export menu from within your book by entering the Reading mode).
3. Accept the incoming book
From the receiving iPad, you'll have to tap Accept and then choose which app you want to open the book in. Choose Book Creator if you want to keep working on the book. Choose iBooks if you just want to view the book.
From the blog:
These articles contain examples of how AirDrop can be used.