photo library multiple clouds

Yes, but for ease of use the libraries should in in separate user accounts on the Mac. That way your husband doesn't have to log out of the joint Apple ID and log into his Apple ID whenever he wants to use the nature library.

With fast user switching he can easily log into the other user account which is already logged into his own Apple/iCloud account and use the library there.

OT is right. You will need two separate user accounts on the Mac. For each user account you can only have one System Photos Library, and only the System Photos Library can sync with iCloud Photos. It will be synced with the AppleID that is set up in the System Preferences/Settings.

The Shared iCloud Photos Library is agreed new feature, but you should be aware, that only the photos and videos will be shared to the Shared iCloud Photos Library, not the albums and folders. It will help, if you tag the photos for each album you want to share with the album name as the keyword. This way you will be able to recreate the albums shared to you as smart albums with the smart rule "Keyword is ...".