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This is required to initialize a group FaceTime call. Press on the new message button in the corner of Messages, and add contacts to the group chat. Make sure that all the numbers appear in blue.  FaceTime only works with iMessage.  Wait for everyone to join.  You will see their faces. On iPhone X or later (excludes iPhone SE (2nd generation)), tap on the star, then choose the Memoji you want to use. You can also tap the star to draw on the camera, add stickers, and more. Tap on the triple dots to expand additional options for your FaceTime call. You cannot end the call, but you can leave the group call by tapping on the x at the bottom. Once everyone has left, the FaceTime call will end.

Summary:
Make sure you and your friends are running iOS 12.1 and later or macOS Mojave with the latest updates. Start a group chat in Messages. Tap on the arrow by the newly formed group. Choose "FaceTime". Turn on your Memoji. Flip the camera, mute the mic, turn off your video, manage who is on the call, and change the audio source. Leave the FaceTime call.