TelemetryTV is able to show live video streams using the Live Video app, However you'll need to enable your UniFi cameras to enable streaming of their video so it can be embedded in your playlist.
There are two methods, depending on how you want to deploy your solution.
Streaming Direct From UniFi Protect Controller
In order to use the method you MUST be using TelemetryOS. RTSP streams are not supported on other platforms.
You can stream direct from your UniFi Controller. This has the limit that your TelemetryTV devices must be able to access directly to the controller over your internal network which is likely limited from access from the Internet.
You should be able to connect multiple displays to a single camera, however for the exact limit of RTSP streams you'll need to consult with Ubiquiti, it's likely hardware dependent.
To get your stream URL for TelemetryTV to use you should login to UniFi Protect and select the camera you want to stream and go to Settings -> Advanced and get the URL for the stream. We recommend using the Medium or Low resolution stream for performance purposes.
Once you have this URL you can paste it in to a TelemetryTV Live Video app as the URL for the app. You should then be able to include this app on a Playlist Page and video the contents of the stream.
You can have multiple cameras shown at once by placing each Live Video app inside a different zone.
Streaming Through a Re-stream Service
You can use a service like https://rtsp.me/ to create a link to view your camera. Please note that you'll need to enable rtsp.me to access your camera from the Internet. Please consult the UniFi documentation on how to do this and be aware of the security implications. Take this link and place it inside a TelemetryTV Website App as the URL. This method should work on any TelemetryTV platform including TelemetryOS.