Clients can't sign up for an appointment that another client has booked in your Pike13 business, but you can take either of two approaches to set up semi-private appointments:
Configure the semi-private appointment as an appointment
One client can book the time slot online, and then a staff member needs to add additional attendees on the staff side.
Configure the semi-private appointment as a class
The schedule needs to be set, but multiple clients can enroll in the semi-private appointment on their own.