Your Premium subscription comes with three extra accounts to share with friends and family. Go to your My Post account, click on the "My Benefits" tab, click the "Share extra accounts" button, and enter the email addresses for the people you would like to share access with. They will be sent an email message and will need to click through it to activate their access. Each user will have a separate login.
Only the primary account holder will be able to view and edit the full range of account details, such as billing and subscription information.