Hey. I have a similar issue which might be solved [IF] Apple would post a thread to explain how to actually initiate a group call/video chat using macOS. There are several posts on YouTube demonstrating how to initiate group Facetime calls on 1OS devices but zero exist for how to using a Mac with Mojave installed. Logically, subscribers to a group Facetime video or audio chat on Macs all have to be running macOS 10.14.1 at least for it to work. Just guessing. It seems that this issue is of a low priority currently.