If you want to stop users sharing the same username/email and password between multiple people, all logging into your site with the same credentials, then this can be done with WP User Manager.
To do this, you need to have the Security addon installed.
- Navigate to User > Settings
- Click the Security tab
- Turn on the ‘Prevent Concurrent Logins’
Once enabled, if a user is logged into their account, then the same account is logged into from a different device from a different IP address, the existing logged in session is removed, preventing concurrent logins.