We don’t provide any customer OEM solution. Maybe you could look for the products from our partners.
For the camera connection, you can check the ecosystem poster.
It is pretty much plug-and-play.
Check the compatible camera list from this topic:
Camera not mentioned may be unusable or untested.
In the current stable Herelink only supports display 1 video stream at the same time.
For the FPV camera, you may check ardupilot wiki for the setup
https://ardupilot.org/copter/docs/common-fpv-first-person-view.html
I shall clarify that the 3rd camera uses another additional piece of hardware other than the Herelink. As mentioned Herelink only supports 2 video input and 1 output at the same time. I’m just telling how you could integrate more camera into your system.