Please make sure to sign in to all devices with the same Apple ID before you can access your books and audiobooks on these devices. The specific steps are as follows:
1. Books purchased from the iBooks Store will automatically appear in iBooks applications on all your devices. Audio books purchased from iBooks Store or iTunes Store will automatically appear in iBooks application on iPhone, iPad or iPod touch with iOS 9 and later, and in iTunes on MAC with iTunes 12.4 or later.
2. If you use iCloud cloud disk, you can access the imported ePub files, iBooks Author books and PDF files on all devices.
3. You can also use iTunes and USB to manually synchronize audiobooks that are not purchased from iTunes Store.
If you join "Family Enjoy", you can enjoy the purchased content with other family members.