If I purchase the $2.99 iCloud storage plan which allows my family to share the 200GB, can my photos be isolated from other family members and can I access all data or just the data from my devices?
iPhone SE, iOS 14
You can only access your own data (data for your Apple ID). 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.
You can only access your own data (data for your Apple ID). 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.
How does sharing work with family and iCloud storage
