Have you heard the news yet? Twitter has made an update that allows for group messages and uploading video straight from the Twitter app!
For group messaging you can message people that follow you, but even if all people within the group do not follow each other they are all still a part of the group message. So it all starts with the person who creates the group! Here is a quick video from Twitter about group messages:
New! Use Direct Messages to speak privately with a group of up to 20 people. Share Tweets, show emoji & be yourself. https://t.co/8giGhC6OO0