The group video chat supports up to four people at a time. And the video will expand as more friends join the conversation.
Once a video chat goes active in a group thread, the camera icon turns blue. To join an active conversation, simply tap on the blue camera icon. Once you are done chatting, tap on the red phone icon at the bottom.
Blocking users will prevent them from being able to video chat with you. Plus you can mute users if you do not want to receive notifications from them. And you can also control video chat notifications by tapping on the gear icon on your profile and scrolling to the new video chat control in Push Notifications.