iCloud storage

Family sharing doesn't automatically share storage. If you want shared storage, see: Share iCloud+ with your family - Apple Support

What does it show when you do the following from Share iCloud+ with your family - Apple Support ?

See how much storage your family's using

Use the steps below to see how much storage your family is using and upgrade if you need more. 

If your family is low on iCloud storage, all members get a notification. Then the family organizer or family member that purchased the plan can buy more—up to 2TB—at any time.

On your iPhone, iPad, or iPod touch

1. Go to Settings > [your name].
2. Tap Family Sharing.
3. Tap iCloud Storage.