You can add team members to your project on the portal by scrolling to the bottom of your Project Dashboard, adding the email address of the person you wish to invite, selecting their role, and then clicking “Invite” – this will send an email invitation to the project.
When they click on the link in that email (or when they visit the portal when logged in under that account), they will receive a prompt to accept or decline the invitation to that project.
You can also adjust the roles of existing team members under Manage Team. There is no limit to the number of administrators a project can have.