Cancel apple one premier
How to cancel apple one premier and separate the accounts under it
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Leave Family Sharing - Apple Support
The associated Apple IDs may or will have to acquire iCloud+ subscriptions.
I’d likely purchase the iCloud+ storage subscriptions first, before disbanding.
Archive or make copies of the information you store in iCloud - Apple Support
Here’s some info on how to shuffle your data around (different cause, though same basic problem):
Can I merge two iCloud accounts - Apple Community
