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 in to 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 Use FaceTime on Mac.