I’d go for HLS due to its simplicity: just files over http(s). VPN or not - depends on your network. If your machine is accessible from the internet, just putting the files into a webserver subdirectory with a long random path and using https will be secure enough for the usecase. Can be done with an ffmpeg oneliner.
The downside of HLS is the lag (practically – 10s or more, maybe 5 if you squeeze it hard). It is in no way realtime. Webrtc does it better (and other things too), but it is also a bigger pain to set up and forward.
Also, just in case, test that the webcam works fine if left active 24/7. I had (a cheapo) one that required a powercycle after a week or so…
Nope. Where I live employees’ salary is included in the food prices.