Hello helsingmorningside,
It sounds as though you're having issues sharing your iCloud+ subscription with your family.
Make sure it's set up as follows: Share iCloud+ with your family
Share iCloud+ with everyone in your family
To share iCloud+, you need iOS 11 or later, iPadOS, or macOS 10.13 High Sierra or later. For the best experience, make sure that your family members' devices meet these requirements, too.
Learn what to do if a family member already has iCloud+
On your iPhone, iPad, or iPod touch
In iOS 16 or iPadOS 16 or later:
1. If you haven't set up Family Sharing yet, set up Family Sharing.
2. Go to Settings > Family.
3. Tap Subscriptions.
4. Tap iCloud+.
5. Follow the steps to share your existing plan.
6. Use Messages to let any family members with an existing iCloud+ plan know that they can now switch to your shared iCloud+ plan.
In iOS 15 or iPadOS 15 or earlier:
1. If you haven't set up Family Sharing yet, set up Family Sharing.
2. Go to Settings > [your name].
3. Tap Family Sharing.
4. Tap iCloud+.
5. Follow the steps to share your existing plan.
6. Use Messages to let any family members with an existing iCloud+ plan know that they can now switch to your shared iCloud+ plan.
Given the detail in your post, we believe you'll need to follow step #6 to send the family a message to notify them they can switch to your shared iCloud+ plan.
In case they were already using an iCloud+ personal plan and need to switch to an iCloud+ family plan:
Switch from your personal iCloud+ plan to your family plan
When you share iCloud+, any family members using the free 5GB plan are added to your family plan automatically.
If a family member is already paying for their own iCloud+ plan, they can choose to switch to your plan or keep their own and still remain part of the family. When they switch to the shared family plan, they get a refund for the remainder of their personal plan. They can't keep their current plan and use the shared family plan at the same time.
On your iPhone, iPad, or iPod touch
In iOS 16 or iPadOS 16 later:
1. Go to Settings > Family.
2. Tap Subscriptions.
3. Tap iCloud+.
4. Tap Use Family Storage.
In iOS 15 or iPadOS 15 or earlier:
1. Go to Settings > [your name].
2. Tap Family Sharing, then tap iCloud+.
3. Tap Use Family Storage.
Let us know if that helps out, take care.