Moving multiple photos from mini macs / existing iCloud’s to a new shared iCloud,

I’m looking to upload all my photos from an old mini Mac to a new 2TB iCloud storage under my iCloud account (which also has Apple one and Apple music).

This old mini Mac has been shared with other family members with 80% of photos stored are on another family member iCloud id and not my iCloud id).

If I opt to extend my iCloud storage 2TB, then how easy is it to move these 80% of other photos?? I assume (I’ve read) that the 2TB storage can be shared across family members. What if these member have separate iCloud id’s?

Also, the same 80% family member has a small £1 / month storage extension (overflow storage for an iPhone). How do I get these iCloud files over to my new iCloud 2TB storage? Then I will cancel this storage as 2TB is plenty for the entire family.

Then, once the 2TB is up and running, I assume family members will have full access to photos and that each device can be configured to upload to the new 2TB iCloud?

Any advice or feedback appreciated.