You are both right. Everyone needs a microphone (actually in some arrangements you can use one between two or three, depending on how reverberant the room is), but only one microphone should be open ('on') at a time.

To  set up this type of hybrid session needs careful design, especially where the ideal equipment is not available. But it can often be done. For example, in some room layouts, one or two 'roving' microphones are practicable, in other layouts not.

Hi Sandy

My initial research does not support what your tech expert states. Audio setup is crucial in hybrid meetings not only so everyone can hear, but to eliminate feedback. In actuality, you do not want more than a single open microphone at any given time. 
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Alan Katsura
akatsura@...
Moderator HLAA Tech Group

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