iCloud and iPhoto use with two users and a shared library

Is your iPhoto Library on an external volume?

iPhoto and Photos are strictly single-user applications. An iPhoto Library or a Photos Library can only be shared between user accounts, if the library is on a volume or in a partition, where the "ignore ownership on this volume" flag has been enabled. (Move your Photos library to save space on your Mac - Apple Support) Otherwise the library would continually have to be repaired because of problems with the file ownership of the internal database files, after the other user opened it.

It is not easy to share the iCloud Photos Library at all between users. The problem is, that only your System Photos Library can be enabled to sync with iCloud. And your System Photos Library will always be in use by the Photos background processes while you are logged into your user account. So you would have to log off, before the other user can access the photos library. Otherwise you will get "Library in Use" errors. Whenever the library needs repairing because of permission conflicts, related crashes, or similar, it will result in a complete new upload to iCloud Photos, which will be tedious and time consuming.

It would be much safer and easier to use two separate Photos Libraries with iCloud Photos. Then you both would be able to remain logged into your account at the same time and Photos could continually be syncing with iCloud.

To save storage on your Mac you could use the option "Optimise Mac Storage". The originals will all be stored in iCloud, but Photos will replace high resolution originals on your Mac by smaller optimised versions, when the storage gets low, so you will only need storage for the optimised versions for browsing.

iPhoto library is now as photo library , you and your wife has admin accounts in users and groups say yours as " A " and your wife as " B " , your admin account account is on the top list , you are using same Mac , the profiles images can be different for both of them but signing in with Mac is common for both , the admin password is revealed , Apple ID and password that is only signed in Mac system preferences is known to each other .

However if you need some or selected photos to be transferred from account A to account B can be done .

If the status for two already created users is an admin account , in users and groups , the Apple ID and password , admin account password is known / common and can be used by both accounts , the photos can be viewed from both accounts , if you turn photos box in preferences , the photos will not be duplicated .

The photos sync from Mac system preferences > when photo box is turned as on , it will reflect in the same way for both accounts .