Yes, your clients can book multiple seats at once for an event. To enable this, set the maximum number of seats that can be booked at once in the group service editor. On the booking page, clients can then select the number of seats they wish to book. Once a booking is made, you can view the number of seats booked by clicking on the event occurrence in the calendar and scrolling down to the list of attendees. The number of seats booked by each participant will be displayed next to their name.
If needed, you can also edit this information by clicking on the participant's name and overriding the number in the "Booked seats" field. Once you're done, save the changes for the participant then for the occurrence as well.