Can you create a single library of photos which have been taken on two different iPhones using different appleIDs?

The image capture app (already on your mac) is just a simple app to transfer photos from external devices (cameras, phones, memory cards) to a folder. It is not referenced to any apple ID.

So it should just work. Hang on, I'll try it...

Hi - unfortunately, no, there isn't.

All automation goes via iCloud/photostream - which is always linked to a particular apple ID.

Photos as a system is not really set up for a sharing libraries. There is a workaround of putting the library on an external disk, and each using your own apple ID/account on the mac to access it. But it is fraught with compromises, and I'd not really recommend if it, if you can live with manual transfer from your wife's phone to the mac.

Incidentally - a better way than air drop might be to use the image capture app on the mac (with a wired connection) to transfer photos from her phone to a folder, and then import to photos from there.

yes, worked perfectly - and I've just transferred all my wife's pictures from her phone to a folder, ready to go into my library.

Note though - that if she used iCloud photos, and sets optimise phone storage, it will only transfer the preview sized images from her phone. If this is the case it would be better to download her images directly from icloud.com