When in budget situation for conference call

• AV system has Vocal Microphone
• Local participants spread over conference room
• Computer is connected to AV system
  and hardened to prevent tampering from non-computer-literate users

With poor audibility from vocal microphone, I’m wondering what if local participants use:

• Computer Zoom App connected to AV Projector Screen and Room Ceiling Loudspeaker. 
• Own Smartphone App for Microphone 

When Virtual participants speak, local participants view and listen via AV Projector Screen and Room Ceiling Loudspeaker ; mute own Smartphone (Audio and Video). 

 When one of the local participants speak, 

• Walk over to AV system to lower Room Ceiling Loudspeaker Volume 
• Unmute his/her Smartphone Zoom Audio
• Other locals use his/her Smartphone Zoom to listen
• Everyone view via AV Projector Screen

The main disadvantage is hearing un-synchronised Sound from neighbouring Smartphone Zoom; will connecting Smartphones to same WiFi network improves sound synchronicity?

Is there a better alternative? 

Our meetings have ~100 participants at a time and the participant entry/exit chime can get really annoying throughout the meeting. I kind of don't want to tell the host (my boss) if he can change the settings (I doubt he knows how to), hopefully this feature can be shifted as an option for participants to toggle with on their end instead of it just being the host's option to change. The host probably doesn't know that he can even change in the settings that both participants and hosts can toggle this option. I think it should be available to everyone regardless of the host's decision because it's really annoying and distracting. Thank you for your time and consideration

I use Zoom to do speech therapy, telehealth online with preschool children.  When I screen share videos with audio or activities with audio, the parents are telling me they cannot hear anything or that it cuts in and out with the audio.  Is this my PC or is this a Zoom issue? How do I fix?