Greetings, Rach_an.
Welcome to the Apple Support Communities. Being able to add people to a group FaceTime call is vital, so we can understand why you’d want a resolution.
First, ensure that you are following these steps when adding a person:
"Add a person to a Group FaceTime call
- From the call, tap the Add button
. - Tap Add Person.
- Enter the contact's name, phone number, or email.
- Tap Add Person to FaceTime.
When you add someone to your call, you can tap Ring next to their name so their device alerts them of the incoming call.
When someone is added to a Group FaceTime call, they can't be removed from the call. The person who was added to the call needs to end the Group FaceTime call.” Use Group FaceTime on your iPhone, iPad, and iPod touch
If so, check out: If you can't make a FaceTime call on your iPhone, iPad, or iPod touch
We hope this helps! Thanks for being a part of the community.
Sincerely.