You can also see a matching color cursor indicating where each person is working in the Document. When each person is actively editing the document, the person's name will be shown on their cursor.
Google Documents allows you to chat with all of the collaborators working in the Document. Click the "Chat" icon next to the icons of the collaborators to open a group chat.
The chat window will appear in the lower right of the Document. You will see the names of all of the people who are part of the chat. Type your message at the bottom of the window and press "Enter" on the keyboard to send it to the group.