See the following from Share an iCloud storage plan with your family - Apple Support
When you share a storage plan, your photos and documents stay private and everyone keeps using their own accounts with iCloud—just like when you have your own storage plan. You simply share the space available in the iCloud storage plan with your family members, so you only have one plan to manage.
It isn't what you are looking for but Family Sharing creates a shared photo album and any photos added to it are shared. See the following from Family Sharing - Apple Support
When you set up your family, a shared album is created automatically in the Photos app on all family members’ devices. Everyone can add photos, videos, and comments to the album whenever they like and get notified when something new is added.