Can I screen share an OS X computer to several viewers over VNC?
To the best of my knowledge the answer to your question is 'No'. I do the same thing and I use GoToMeeting or GoToWebinar. They are commercial products that cost money but they work really well. (I'm not affiliated in any way... I just use their products). I give demos all the time with GoToMeeting. The monthly fee was totally reasonable for what I do.