If several participants will be using audio, then you can select Enable Single Speaker Mode from the Audio menu. This setting will prevent participants from talking over one another. When one person has pressed down on the talk button, other participants will not be able to press their talk button.
If you notice an echo, then this is a telltale sign that more than one person has their microphone set to Hands-Free and their microphone and speakers are separate. Their audio is going through their external speakers and traveling back through their microphone causing an audio loop. Using a headset can help reduce the chances of this happening.
