Apple appears to have disabled the Group FaceTime feature while they work on a security update. Yesterday, a bug was discovered that allow anyone to listen to in on a person’s iPhone microphone simply by placing a FaceTime call. The bug allows for some pretty scary scenarios ranging from listening in on conversations to being able to see people in compromising situations. Apple has not confirmed that this is the case, but there has been no public announcement from Apple indicating that this may be the case. BleepingComputer has reached out to Apple for confirmation, but had not heard back at the time of this publication.
Source: https://www.bleepingcomputer.com/news/apple/apple-disabled-group-facetime-while-working-on-bug-fix/