Facebook has announced group video chat in Messenger. It is available today with the latest update on both Android and iOS devices as well as the desktop version of Messenger.
To use this feature you need to start or join a group conversation. Press the video icon on the upper right of the screen and you’re in! You can see up to 6 people, including yourself, at the same time. Once you have more than 6 people (up to 50!) on the call, only the dominant speaker is shown to everyone.