How to Use iCloud's Family Sharing with Photos for OS X?

You can not sync your entire iCloud Photo Library with your family member, but you can share your photos with them. There are 3 ways to share your photos with each family member. You can use Family Sharing's Family album to share your photos or you can use iCloud Photo Sharing to share your photos or you can share an iCloud ID with your family members to share your photos.

If you want to use Family Sharing's Family album to share photos, then you need to enable iCloud's "Family Sharing" option along with "iCloud Photo Sharing on your device. When you enable "Family Sharing" on your OS X, you will see a special album called "Family" in the "Shared " tab of the Photos for OS X app. If you enable it on iPhone or iPad, you will see it in "Shared" section of the Photos app. This album will automatically sync with all members within your Family Sharing group.

If you want to add photos to the shared stream, then select the photos and click "Share" button. Now, choose "iCloud Photo Library" option and then select "Family" album. Your photos will then sync to your family member's device. If you want to add your family's photos from this shared stream to your "Photos" library, then you will need to turn ON the sidebar in Photos app. To do so, open "Photos" app, Click "View" menu bar and select "Show Sidebar" option. Browse to your shared stream and select the photos which you want to add to your Photos library. You can drag them to the Photos entry in the sidebar.