There are a couple ways. First, be sure to go to the Settings app on your iOS devices, scroll down to iBooks, and turn on Sync Collections.
1. If you use iCloud Backup and have all of the devices on the same account then they should sync.
2. If you set up iTunes Wi-Fi Sync for each device then it should sync your books whenever iTunes is running on the master computer and you plug your devices in to charge (or manually tell them to sync).