I don't know but Skype can be done using a computer, so I assume a different one (or a mixed AV signal) would work via USB. Fred would be a better person to ask.

I could be wrong, but the person I know who did the live shows on the last two Fridays may have used an iPad, but I'll ask.

On FB Live, people can leave comments in real time and the presenter is able to read/respond to them. I know a musician who has been using that to get his music out there and communicate with his fans- sound isn't amazing, but it's clear and decent.