Kempten, Bavaria to Salzburg

And is it possible to use a Bayern Pass for multiple people going for a weekend?

Sure, takes twice as long, costs more, has more connections, but you can go via Bregenz, or take a bunch of local connections through Seefeld and Innsbruck.
But not with a Bayern Ticket.

Thanks, Sam! If we go through Munich, can we use the Bayern Ticket?

If we go through Munich, can we use the Bayern Ticket?

Yes, as long as you use regional trains. No ICE, EC, or IC. But most connection are all regional, and there is little or no time advantage to using an express train. And you can only travel using the Bayern-Ticket after 9 am on workdays.

It only takes about 3½ hours, but if you schedule yourself a stopover in Munich at around noon, you can eat at the food court in the Hbf.

Find schedules on the Bahn schedule webpage (in English).

you can eat at the food court in the Hbf

The station building is currently being demolished, so you certainly would want to look out for a more pleasant place. There is a plethora of opportunities not far away.