The idea is to use a RasPI 2B connected to their TV, a Logitech c920 camera connected via USB to the RasPI, and appr.tc or jitsi.org as WebRTC server for the chat. Using this setup, I can simply open an url in the RasPI browser, like https://meet.jit.si/TestCall, and connect them to a WebRTC room, while I can use my PC or any other client as the other side of the chat.
Why Logitech c920? Because it's supported out of the box on Raspbian Jessie, has a wide-angle len very good for videocalls, has a good directional mic and can produce an hardware encoded H.264 video stream, so no CPU overload.
Regarding the browser to use, I tried Iceweasel first, but is not working well on appr.tc and version < 40 is not supported by jitsi.org (Jessie has v38 on the repo).
So I installed Chromium using the Ubuntu repository and this link or this link, both very similar.
With this setup, the WebRTC videocall starts correctly, I have both sides connected, audio and video working and I'm an happy man!!!!
Unfortunately, after 30 to 60 secs, audio from the RasPI side stops working, and only the video is transmitted. I can see video from the RasPI side, but I cannot hear the audio. Instead, on the RasPI side, it's possible to see and hear my stream.
I don't know where the problem can be...

* Browser side? I tried Iceweasel, Chromium v43 and v45 (because v47 has a very bad bug that influence video render), bot nothing has worked properly.
* WebRTC server side? Tested appr.tc, jitsi.org, opentokrtc.com and others: when I was able to connect, I always had the same audio problem, as soon as connected or later during the call.
* RasPI OS side? Tried Jessie with latest drivers, as soon as I've time I want to try also Ubuntu Mate, but I feel this is the wrong way.
In any case, very sad about the experience with WebRTC implementation on different browsers: it should have been the "best of new portable web experience", right now I feel back to "work on my pc" era....

If not WebRTC, what other videocall solutions do you suggest? Please consider that no user interaction should be required RasPI side to start the call.