No need for you to be sorry @katalinhausel
In an attempt to reclaim my data sovereignty I've been using QubesOS which, for security reasons, is designed not to play nice with USB. I have an old USB video camera and knew it would take me a bit of time to get something up and running. I (foolishly?) estimated an hour but I didnt get started much before the call was scheduled as I went to help a friend with some emergency plumbing.
chr0no has been developing a text/video conferencing tool He's an opensource proponent so is only supporting Firefox and Chromium. He says it works best with Chromium also works with latest smartphones. Uses webRTC, same as Hangouts and the video calling tools that have recently been appearing (lots of web based one + Mozilla Talk). All the video goes p2p rather than via his server. How many people in a call depends on the power of the devices in use - he says about 8.
I've only tried it twice, a month or so back, a test call to a friend which worked well with us both using Iceweasel (Firefox) and a 6 person conference call with unknown devices/software in use - which didnt work.
Looking for a robust/easy to use video conferencing solution recently for webinars by a project I'm part of, which potentially could attract quite a varied demographic, I came to the unfortunate conclusion that, at least at the current time, we would have to use Hangouts or Skype.
There are other possible options if you can get people to install software or have a server and someone to set it up. Also more options coming fairly soon I think.