I've been sharing my Apple ID (I'll call it A) details with my wife for many years, in order to share app purchases.
We'd now like to switch to Family Sharing. My Apple ID A would be the "family organizer".
After setting up Family Sharing, my wife would set up her iPhone (in Settings > iTunes & App Store > Apple ID) to use her own Apple ID ("B"). This ID currently has no purchases.
What will happen to her existing apps, some of which have saved local data?
Reading around a bit, perhaps we'll run into this sequence of problems:
The existing apps might still be marked as "purchased by" A. If my wife wants to update them, she'd need to enter the A credentials (source)... I guess this is OK, but not ideal.
To fix that, perhaps we could delete the offending app and then re-purchase it using her account B (which is now linked to A via Family Sharing). Updating it then requires her B credentials, which is fine.
But then presumably we'll find that the app's saved local data has been deleted by the reinstall. Perhaps we could then use iMazing to restore the app data from an earlier backup (source).
Have I understood this correctly?