Within Teamwork.com, you can add people to projects as observers, giving them project access without making them primary participants.
Note: Only owner company standard users can be set as observers on projects.
Go to the People area of your project and select the People subsection.
In the list of project members, click the user icon to the left of the relevant user's name to make them an observer.
The observer shield will display in purple for any observers on the project.
You can also make someone an observer by selecting Edit Project Permissions from the options menu (three dots) to the right of the users name in the People area of the project.
At the bottom of the user project permissions modal, click Show Advanced to reveal additional options. Toggle on Is Just an Observer Here to make the user an observer on the project, then click Update.
Note: Only site administrators or users with permission to manage people and companies can make someone an observer on a project.
For more information, see: Observers