Can I share iBooks with another device that is authorized for the purchasing account?
iBooks, like all items bought in the iTunes store, can be shared across different iTunes libraries via iTunes Home Sharing. As Apple states:


  Home Sharing in iTunes is designed to let you easily share your iTunes media libraries between up to five computers in your household.


All libraries setup for sharing with the same ID can import purchases made with that ID, independently of the ID they normally use for purchases in the iTunes store. See Apple Home Sharing Support for details on requirements, setup procedure etc.