When I go to https://wpamelia.com/appointments/ I see this:

There are two different types of appointments each of which is based on the maximum capacity of the service that is delivered. An appointment is considered as a “Single” appointment if the maximum capacity of the service is 1. If the maximum capacity is higher than 1, the appointment is considered as “Group”. There are two types of group appointments:

• Group appointments where all customers are separate (usually the case when they don’t know one another).
• Group appointments where one customer defines a number of persons that are coming with him or her.

The main difference between these two is that in the first one every person appears in the appointment separately, with all details defined, such as name, email, appointment status, payment details, etc.; this means that any person can cancel his/her participation in the appointment separately.

The situation with the second type of group appointments is that only the person who has scheduled the appointment has a name, email, appointment status, and payment details. The others are seen as +1.. +10 “addition”. So if one of them decides to cancel his or her participation in the appointment, there are two options: either they will cancel for all, or you need to reduce the number of persons in the “Edit Appointment” dialog.

I have occasions when someone will want to book an appointment with me and several people will join the appointment.  For me it would never be the case that they wouldn't know each other and generally one person would book it so I think either of those options would work for me.  What I really want is probably the second option though: one person books a slot and has the option to add usually one more person with their names and Email addresses and for all of them to get the pending message and the approved message (or the refusal).  I have increased the number of possible attenders but nothing seems to happen to the booking to allow someone to add other identified attenders and I can find nothing else in your online docs that explains either of the alternatives you describe there.  

I am very frustrated by how much time I seem to be wasting with Amelia.  At the moment it's a tool that is supposed to save me time which is costing me much more time than it is saving.