Juli Clover, writing for MacRumors:
An iCloud Shared Photo Library can be shared with up to five other people, and each contributor has equal access to add, edit, favorite, caption, and delete shared photos.
To prevent accidentally shared photos, there are smart setup rules that can be implemented. You can opt to share all past photos or just photos from a specific start date. You can also choose to share photos that have only specific people, such as your family members.
Photos can be added to the Shared Library automatically, but there are also options to share based on Bluetooth proximity. Sharing suggestions will continue to pop up in For You as well.
My wife and I have been using Google Photos for years specifically because of their partner sharing feature. But I look forward to kicking that to the curb and using Apple’s offering instead.