That’s how to do crisis response right 
Glad you two could pull this off so quickly. It’s what I have seen them do in Nepal after the earthquakes much better than Europeans in the pandemic: recognizing what tools and opportunities are there, and using these in a pragmatic manner. In Europe, I get the impression that most of us just don’t know how to respond …
As for the tech questions:
Hmm. It’s true that you won’t get a decent video conferencing system for any meaning of free. The widget in now.edgeryders.eu however is not free, either: it’s using the paid plan of daily.co, a good video conferencing API. We haven’t tested it to capacity yet, but they claim “Participants in room: 200”.
As far as I’ve heard from @owen, it does not rely on WebRTC when there are more than a handful users in a room. And then – if they provide a backbone server just like Zoom – I don’t really see an a priori reason why video conferencing in a browser is impossible to get right? Browsers can play video alright, and if that’s what they get served from the backbone server (as one combined video, perhaps), it should just work … . But yea, we didn’t test that much. You’d have to try.
The interesting aspect would of course be that you can embed the video conferencing widget into your open source website. A single paid component that can be exchanged if needed is quite a different dependency than a fat proprietary tool that people have to install. Zoom under Linux is ~300 MiB, which I consider an insult.