I'm running into same thing... a not so easy answer is to select the shared photos and then right click and there is an option to save shared photos. once saved they are editable and I'd think searchable (faces, etc)... The trick is how to pick out the shared photos in your library.
I see three things: 1. in the icon library view the shared photo's have a speech bubble in the lower left corner. 2. In the large view, if you double click on one of the photo's, it will show "shared from" in the top center. 3. also the info pop up window shows which phone took the shot.
So from what I see we have to pick/ command click the shared pics and then right click and save the photos (to my library).
The "filter by" (at top right) allows me to turn on/off the shared photos but that doesn't help to separate, or select them.
ANSWER! If spouse photos are with a distinguishable iphone you can search for that... I used to have an iphone 11, now got a 13 but wife has "iphone 11 pro max" so if I search for that then only those pics are there and I can save them all at once!