[GNOME] Three computers in audio conference call (no video) with 2 unique usernames not working

Issue generated from Tuleap's migration script. Originally submitted by: Óvári (ovari)

The three computers all have the same setup being:
Linux Mint 18.2 Cinnamon 64-bit
Ring 1.0 built on 2017-08-03 21:36:55 UTC

 1. Setup:  
    (a) Computer with username: same  
    (b) Computer with username: same  
    (c) Computer with username: different  

 2. Please advise how to do a conference call in this configuration.  

 3. Please advise if you require any additional information.  

 4. Please advise when this feature has been implemented for testing purposes.

Thank you