Is it possible to simultaneously connect two pairs of AirPods with my Apple Watch (series 3)? This would allow me and someone else to listen to the same music, podcast, Audible book, etc.
No this isn’t possible and is a limitation with Bluetooth.
No. Unfortunately this is a limitation of the Bluetooth Standard. Only one device of a specified type of connection can be used at a time through bluetooth. So while you could use Airpods, an Apple watch and a Bt keyboard with an iPhone all at the same time you cannot use more than one of each at a time.