Unable to do group video call and group screen share using Skype 4.3

Solution 1:

Skype does not support those features right now on Linux. I emailed Microsoft a couple weeks ago, on this very issue, and they have said that Linux Skype does not support those features at this time.

There are numerous Skype community forum threads on this, and it appears that those features are available on Windows but not Linux.

As of October 23rd, 2015, when I last tested this, group video calling (aka "Video Conference Calls") are not supported still. Group voice communications are still possible, but not video communications in a group chat on Skype. Screen sharing is also not supported still either.

Solution 2:

As said by Thomas W.'s answer, video conferencing/group video call is unsupported on Skype for Linux.

Video conferencing works on Skype for Windows. You can install this on Ubuntu using PlayOnLinux/Wine, but it requires some fiddling...