You can add as many users as you want for a project. Browsee does not charge you for adding extra people to your project.
Go to Account page from left panel
Go to "Team" tab for adding users to the project
Click on the "Add Users" button to start adding users or inviting new users on the project
Type the emails for users separated by comma and then click "Send Invite" to add them in the project
If you have added a new user (having no accounts in Browsee), they will recieve an email to accept the invite and create a new account. As soon as, they will create an account, they will be able to see the see and edit the project.