Can two people share the same AirTag

Not at the present time.

However changes are coming this Fall w/ iOS 17.

You can read the public announcement here:

iOS 17 makes iPhone more personal and intuitive - Apple

I would think that 99% of people get an airtag to find a misplaced item and not to spy on others. Therefore it should be a no-brainer to be able to register an airtag to at least two apple ids.