Make a Group FaceTime call on Mac
When you’re on a Group FaceTime call, you can add more people to the call (up to a maximum of 32 participants) even if you didn’t start the call.
Note: Group FaceTime is available with the macOS Mojave 10.14.3 Supplemental Update or later, or iOS 12.1.4 or later. This feature may not be available in all regions. See the Apple Support article About the security content of macOS Mojave 10.14.3 Supplemental Update.
In the FaceTime app
on your Mac, click the Sidebar button 
during a group call.Click the Add Person button
, then enter the email address or phone number of the person you want to call. If you have a card for the person in Contacts, you can just enter the person’s name.Click Add.
Each participant appears in a tile on the screen. When a participant speaks, or you click a tile, that tile moves to the front and becomes more prominent. Tiles that can’t fit on the screen appear in a row at the bottom. To find a participant you don’t see, scroll through the row.
To send an audible alert to a caller who hasn’t yet joined the call, click the Sidebar button , then click Ring.