You can't sync your entire iCloud Photo Library with your family, but you can still share images with them.
While iCloud Photo Library supports syncing your photos, videos, and albums across your own personal devices, it doesn't offer an option to sync everything to a family member's device: After all, do you really want to share every photo or video you've ever taken with your family? Probably not.
As such, if you have Family Sharing enabled, you'll still have your own Photos library. But that doesn't mean you can't still share images with each other easily. Here are three options I've been using to keep my family in the loop.
Use Family Sharing's Family album
If you have iCloud's Family Sharing option enabled along with iCloud Photo Sharing, you'll see a special album called "Family" in the Shared tab of the Photos for OS X app, as well as the Shared section of the Photos app on iPhone and iPad. This album will automatically sync with all members within your Family Sharing group.
To add photos to the shared stream, select them and click the Share button. From there, choose iCloud Photo Library, and select the Family album. The images will then sync over to your family member's device.
If you want to add your family's images from this shared stream to your Photos library, you'll first need to turn on the sidebar in Photos by going to View > Show Sidebar from the menu bar. Then navigate to your shared stream and select the photos you wish to import, and drag them to the Photos entry in the sidebar. Once you do, they'll copy over to your Photos library and sync with iCloud Photo Library, if you have it enabled.
Use iCloud Photo Sharing to share images with your family
If you don't have Family Sharing enabled, you can still use iCloud Photo Sharing to send certain images to your family, while keeping the ones you don't confined to your own iCloud account. Here's a quick primer on setting up Sharing and an album for your family and close friends.
- Make sure you have Photo Sharing turned on. To do so, visit Photos > Preferences > iCloud from the menu bar and click the checkbox next to iCloud Photo Sharing. You don't technically even need iCloud enabled to use this feature — it'll work even if iCloud Photo Library isn't turned on.
- Navigate to the Shared tab and press the plus button in the toolbar. You'll be asked to name your shared album, invite other iCloud members, and add a comment about the album. A word to the wise: You can invite (or disinvite) more people at any time, but once you name an album, you name it for good — so choose something timeless!
- Click Create to start sharing photos with your family members. You can add images at any time from your library by selecting them and clicking the Share button, choosing iCloud Photo Library, and selecting the album you want them to go to.
- The images will then sync over to your family member's device. They can add images themselves at any point by following the same instructions outlined in step three.
If you want to add images from your shared stream into your Photos library, here's how.
- Turn on the sidebar in Photos by going to View > Show Sidebar from the menu bar.
- Navigate to your shared stream and select the photos you wish to import.
- Drag the selected photos to the Photos entry in the sidebar. They'll then copy over to your Photos library and sync with iCloud Photo Library, if you have it enabled.
Share an iCloud ID
This method is far less common in the age of Family Sharing for iTunes and the like, but on the off-chance that you still use a single ID for your purchases, you can unify your libraries by signing into iCloud on each device you want to share photos with, then turning on iCloud Photo Library.
Be advised, however, that doing so will share every photo taken or uploaded from each device — you'll have no way to curate what you want (or don't want) to share.