Panelists Location

I have 4 panelists who think that they can be in the same room during a webinar.  I have never done that and just want to confirm that this should not be done due to sound transfer, especially if one is talking and the others have their microphones on.  I don't want to be messing around with turning mic's on and off.  Has anyone done a webinar with 4 panelists in a boardroom on their own devices?