iCloud storage
Is there any way to share your iCloud storage with only one family member?
See this article:
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.