A single ticket is issued for the whole group, meaning the whole group must be present at the boarding gate. It is not possible to bring in half of the group first and the other half later. For reasons of queue management in a restricted public space, it is also not possible for one member of the group to arrive and then wait for the rest of the group.
Even more so than for individual passengers, we recommend that groups arrive at least 15 minutes before departure time, especially during busy periods.