Q: Family Sharing audiobooks

A Guide to Family Sharing - iCloud - Apple Developer

Sharing purchased content with Family Sharing

Family Sharing and Apple IDs for kids

Family Sharing

How Apple's iOS 8 Family Sharing for iTunes will work

Apparently, you can't, but for some reason Apple is deliberately avoiding any mention of this. It's not listed on any support article regarding what can and cannot be shared.

Audio books are not mentioned as sharable, or non-sharable.  But you are correct that it is not specified.

WHY is it not specified? That seems deliberately evasive on Apple's part. And WHY are audiobooks non-sharable in the first place?

apple.com/feedback , and I don't know why they are not sharable.  Why are some apps sharable, and others are not?  Why are some songs removed from the iTunes store, when others are not? 

Good questions all.

Similarly, BE WARNED icloud does not back-up Audiobook purchases, another thing Apple don't make clear to users. They only back up the last 6 month's of Audiobook purchases, anything you delete before that is lost (in fairness I eventually got them to restore all past purchases, but it's not policy). It's something to do with Apple's rights agreement with Audible and other Audiobook publishers. But it's something they should be more forthright about and clearly something they should be pressured to change.