Family iCloud

When using Family Sharing each family member continues to use their own Apple ID and password to access iCloud. That is true even if sharing an iCloud storage plan. Also 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.