This video shows how easy it is to stream multiple video users to YouTube using OBS and shared screens.
OBS will allow capture of any video call source (like appear.in, zoom.us etc), we can then setup a Scene (like a few google slide show or a Doc) and Go Live.
I've set video quality to 240p as wanted to minimise any dropped frames. Now a low video resolution is successful, then we can dial up and test: 360p, 480p and 720p. On low bandwidth, choose a low resolution (like 240 or 360p) to make sure you message gets delivered. Audio will prioritise over video every time - in other words, if bandwidth is an issue, video will drop frames or pause - where audio will be just fine (this is normal).
The real discussion is WHAT SHOULD WE SEE and HEAR? If this was a learning session, then having 3 video users LARGE on screen will NOT help you learn at all - where the slide is the learning part. Save glorious HD Romanticism for your spare time.
*OBS = Open Broadcast Software.