Hi,
I would recommend setting up Family Sharing on the primary users Apple ID. The primary user, or “Organizer” of the Family Sharing is required to have a valid payment method on file with their Apple ID, and also has to be the one to share the iCloud+ renewal with all the other family members.
This means they will be the one paying for the iCloud+ storage plan each month.
https://support.apple.com/en-us/HT201088
Once the Organizer has been decided, up to 5 other members can be added to your Family Sharing.
To start sharing iCloud+ Storage with your family, on the Organizers device, go to Settings > Name > iCloud > Manage Storage > Change Storage Plan > select the preferred plan to continue:
- 50GB $0.99 USD
- 200GB $2.99 USD
- 2TB $9.99 USD
https://support.apple.com/en-us/HT201238
Once purchased, iCloud+ is shared with your Family.
This means every member will contribute to the available storage in iCloud, but all data backed up and stored will be separated per Apple ID.
iCloud data can only be accessed by the Apple ID user it is tied to, either via device Settings or online at iCloud.com.
https://support.apple.com/guide/icloud/use-icloud-with-your-family-mm0b5e79e99b/icloud
https://support.apple.com/guide/mac-help/change-icloud-storage-preferences-family-mchl40b5b17d/mac
Hope this helps!