Can you add air tag to more then 1 device

You can only associate an AirTag to one Apple ID. As such, any Apple device that is logged in with that ID can "see" the AirTag in the Find My app.

I will add, if you're looking to share this AirTag's location with family and friends, this is a feature that is being implemented in iOS 17 (coming this Fall) - iOS 17 Preview - Apple