They can each speak separately on their own, but if they speakk on different topics, the conveyed information for any of them may be lost by each other. This means that they are not only able to speak, but listen at the same time they are speaking. All of them will speak and listen at the same time. In order to sing in harmony, each singer must be able to hear the frequencies being used by the other singers, and strive to create a frequency with their voice that matches the desiired frequency to create that harmony. This feed-back of each singer to listen to the collective, and possibly key into a specific singer's voice is used by them as they sing to create the exact frequuency needed, and ensure their timing is the same as the rest of the singers.
All members are able to hear all other members, and speak at the same time.
They are all acting as a Full-Duplex communications in a broadcast network. A woman in a resteraunt whispers to her wife a message. Nobody else in the resteraunt know what was said. The conversation was only between one point and another. A single rider takes a bag of mail, and starts riding from the first outpost in a westerly direction until he gets to the second outpost.