What is the best free screen sharing program for groups?

I'm thinking of staring on line courses for a specialized peace of software. Attendees would have to see my screen and when they get stuck I need to be able to switch to their PC to help them out. Ideally, other students could also see what I'm doing on that PC. It would be small groups, 5 attendees or so. They would, naturally, have to be able to hear me and I, and other attendees, should be able to hear them, so when they have a question everyone can participate. Based on real live courses I've held so far, there will be many questions. There is no need for webcam, attendance tracking or other "classroom experience" features. Strictly screen and audio. Windows only required, since software in question is Windows only, Linux fanboys, don't kill the messenger. No time restrictions. Easy to use, some of the attendees may not be tech savvy. 100% free. I can't ask attendees to also pay for screensharing apps. So far, I couldn't find something that ticks all boxes. RustDesk keeps popping up as a popular choice, but apparently audio could be a problem, since that is not its intended purpose.