What Amazon Prime benefits cannot be shared with your household?

As I write this, most Amazon Prime benefits can be shared with a spouse or significant other, as long as you feel comfortable sharing a credit card with them. However, several things cannot be shared:

• Access to the Prime Music library
• Amazon Music purchases
• Amazon Video purchases

It's possible that they're restricting music and video in an effort to keep prices low. I imagine buying a "family license" would cost more than buying a "personal license." Why that doesn't apply to ebooks and audiobooks, I can only guess.