You can add more people to groups at any time by selecting the three vertical dots at the top right of the UI from within the group and tapping People.
If you have a business account, you can video chat with up to 24 other people.
To video chat with multiple people at once, just add up to nine contacts in the entry field when starting a video call.
To message multiple people at once, you can create groups by selecting New group below the contact entry field and adding up to 150 people.
If you start a new conversation with someone who does not use Hangouts yet by entering their email address or phone number, it will send them an invite to use the service.
You can then type in the name, email address, or phone number of an existing Hangouts user to start a text-based conversation or video call.
Tap the green and white “+” button at the app’s bottom right and select either New conversation or New video call.