Photos Backups for Multiple Family Members

I want to back up my Photos library and my wife’s Photos library to external storage, but I don’t know how to ensure hers are backed up without manual intervention. I have a personal Mac to which my original photos are downloaded. I enabled ‘Optimize iPhone Storage’ for my iOS devices. My photos are backed up in multiple ways: - Time Machine (backup of internal SSD) - Carbon Copy Cloner (backup of internal SSD) - Carbon Copy Cloner (backup of `Pictures` directory in which my Photos library is stored) - Backblaze Now, I want to add automate the backup of my wife’s Photos library. However, she doesn’t have her own Mac to which she can store her Photos library. Currently, I’m using iMazing to make weekly manual exports of her iPhone’s photos to my Mac’s `Pictures` directory. Her photos are then part of my backups. In order to automate backups of her photos, do we need a Mac for her, for which I can create separate backups? Instead, can I create a second user account for her on my Mac, and then store her Photos library there? If so, will her Photos library sync automatically with iCloud when her user account is not in logged in (i.e. when I’m signed into mine)? Is there a way that both Photos libraries can be stored in my user account? That would, on the surface, simplify my backup strategy, but I understand that it’s likely to be impossible since we have separate Apple accounts. How can I best achieve a suitable backup strategy for our separate Photos libraries that relies on automated backups? Thank you!