Group Appointments in Appointments

How can I have multiple slots in a single appointment block?

Like 6 openings in one time block, because I'm setting this up for a tour guide. He can take 15 people in a group. The people signup, independently without knowing each other.

The tours take 3 hours each. Two tour guides are running at the same time.

Am I making sense? Do I need to explain further?
I'm just wondering how to set it up.