Hello,
Rates and information on group travel (starting from 10 people) are available on this page.
The SwissPass is actually just the card on which any subscriptions are stored and is generally intended for residents or frequent travelers.
The group discount applies only to tickets. All information on tourist passes is available here instead. Note that if traveling as a family with children under 16 years old, there is the Family Card which allows them to travel for free.
I wish you a nice day,
Chiara_S