Hi,
Not sure if there may already be a feature or setting for this, but just noticed that when I started a group message with a few people, and then mentioned the idea of adding some more people to that, someone in the group was able to invite a whole lot of people to the group message thread without needing to be authorized to do that by person who started the message thread (which was me).
Could be good for there to be a setting so that only the person who starts a group message is able to invite new members to the group talk.