Hey Roy,

iam a bit confused what you want. Because it is a bit confusing to read.

You have a lot of wireless mics. ANd you want something like a intercom talkback that the director (who is using the web controller) can speak to tha camera operators.

Normaly you use intercom systems from RTS or Clearcom to crate a partyline where all teammates con talk to each other.

You can do it with vMix but it is not an good idea to do because of latency. (Usually you hear yourself on the intercom [sidetone/selfmonitoring] but ech tiny ammount of delay make you feel uncomftable and vMix behaves like an software DAW wich had latency and latency is not good for communication.
If i read correctly you want the director talk over the webcontroller tabblet wich is a voip service (more delay)

So an analog mixing desk and or a headphone preamp or headphone beltbacks is the only stuff you will need.

if you are are more into digitaul stuff make an teamspeak server and let all personnel use thier mobile

There are apps on mobiles that act like aan inntercom. Zello is just one to mention. Some phones and apps can be run in split screen. You can have one half for tally and the other for intercom. VLC is able to play SRT streams. You can use that to connect to vmix audio.

So hearing the director is easy with mobiles.

Just send the directors voice to an bus and make an ndi output (you can also send audio inputs per ndi directly)
The cameramen can use a ndi minotor app to listen to him but talking is a bit more complicated.

Be aware that intercom (selfbuild is tricky) is not that easy as you think. Iam not aware if vMix can do a mix minus with audio inputs (like calls do)

So if camera A speaks to direktor and camera B and C and you will lead in hearing him hisself with the delay in vmix wich makes him stutter (i tested this)
To make it good you need one audio bus for each intercom listner and send cam a to output directo cam b and cam c. Cam b sends to cam a and cam c and director and so forth.
The sidetone most be generatet at the taliking side.
You will also need an audio interface with a lot of outputs

The most of the stuff you have is the analog mic and headphone gear. Now you will need a fast mixer. Even a better digital audion interface could be the soultion if it comes with an dsp an independed latency free headphone mixes. But the roundtrip throug the pc will make most people stutter.

Like mavik soid use other apps:
https://www.unityintercom.com or teamspeak, or a zoomcall.

Please make notice that avery streamed audio is useless when you need a sturdy timebase. every network based streming solution will couse timing trouble.
If the dirctor makes on countdown and all need to da specific task in the same moment get sure they hear the command the same time (wich is not possible allways possible)