I think i got it!
if anyone wants to clean this up let me know, it does work though as is
this is the partial code from the windows batch file:
ECHO Type in your stating playlist file
set /p list=""
bin\ffmpeg -hide_banner -loglevel quiet -stats -re -f concat -safe 0 -stream_loop -1 -i %list% ...
We used RTSP and it works fine. There are a few benefits of NDI (like doing PTZ controls over that protocol) but not worth the price jump for the cameras, in my opinion ($600 to upgrade each camera to NDI).
We do notice a ~200 ms delay in the video reaching the mixing PC behind the audio so we just use Vmix to delay the sound and match them up.