Group FaceTime audio and video call requirements
To make and receive FaceTime calls with multiple people (Group FaceTime), you and the people you’re calling must meet the following requirements:
Be connected to the Internet
Be signed into FaceTime with your Apple ID
Have a built-in or connected microphone; for FaceTime video calls, you also need a built-in or connected camera
Have one of the following:
macOS 10.14.3 Supplemental Update or later (See the Apple Support article About the security content of macOS Mojave 10.14.3 Supplemental Update.)
iOS 12.1.4 or later
This feature may not be available in all countries or regions.
See the Apple Support article Use FaceTime on Mac.