Swapping Macs

Each of you should "sign out" of all iCloud products and services on the Mac you no longer want to use. The remaining user will remove any redundant User Accounts: Delete a user or group on Mac - Apple Support.

Following What to do before you sell, give away, or trade in your Mac ensures none of the other's content or purchases will remain.

Log in to the User Account you plan to delete, and follow Step 3 in What to do before you sell, give away, or trade in your Mac. Deciding to keep a local copy doesn't matter because you'll be deleting the Account when you follow Delete a user or group on Mac - Apple Support.

A usual thing to try, would be make second Admin accounts, to work from in this instance.

And have other backups until matter is resolved.

Good luck in any case!🙂