http://www.pcpro.co.uk/news/386134/free-skype-group-video-calls-for-a-year

Even with the release of a GROUP video call now for free (versus only between two parties), Google Hangout still might be the way to go:

http://searchunifiedcommunications.techtarget.com/feature/Google-Hangouts-vs-Skype-A-comparative-look

In addition to Google Hangout, please have more alternatives for video and desktopsharing (mostly free):

9 Ways Students Can Host Peer Tutoring Sessions Online

http://www.freetech4teachers.com/2012/11/9-ways-students-can-host-peer-tutoring.html#.U1J6ZPldWSo