I'm familiar with Skype although I don't think I've ever done a multi-person session - either text or voice.
I've done voice. It works.
I wonder about the practicality of doing a multi-person Skype session that lasts eight hours. I've done a (pardon the expression) shitload of ROV video monitoring. It sounds exciting and it is - for the first 20 minutes or so. If you're really into deep corals, like the folks aboard Falkor, I'm sure it's riveting, but if you're just waiting for something man-made to show up it's BORING.
Understood.
Having someone to talk do MIGHT help pass the time.
Might not.
Skype can do both audio and text at the same time. So can Teamviewer, I think. Of course, watching the text window for comments could distract people from watching the live stream ...
If any of your volunteers want to set it up, the time to practice the conference call and work out the wrinkles is BEFORE the day of the live video stream.
I don't think it should be imposed on anyone who just wants to watch for a while all by themselves.