How can I add a family member
How can I add a family member to iCloud+
Re: How can I add a family member to iCloud+
Seems everyone should use their own Apple ID:
How to Add a family member to your shared subscriptions - Apple Support
More info:
How to: Manage Family Sharing settings - Apple Support
says
"If you’re sharing a Family iCloud storage plan, each person’s files and documents remain private, while the amount of storage space being used by each person is visible to all members".