Hi olemanperk
welcome to the Apple (user-to-user) Community!
Re: Sharing purchased iBooks with family
If you want to check:
See how to: Set up Family Sharing - Apple Support
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Re: "I purchased an iBook on my phone and shared it with my husband. When he tries to download it, it says "you cannot redownload this" - and he does not have access to the book".
Apple support's article: What types of content can I share with my family?
Share content with your family - Apple Support
says:
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What you can share:
Books from the Book Store in Apple Books.
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What you can't share:
Items that are no longer available in the App Store, iTunes Store, Books Store, or Apple TV app.
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You might want to check how to: Redownload books and audiobooks - Apple Support
and
What to do: If there's an issue when you redownload apps, movies, or other content from Apple - Apple Support
Hope something here can help :-)