If you want to add a second (or third, or fourth) organisation under the same personal account, this is easy to do.
Your organisations don't need to be linked to each other - they could be totally different, just both managed by you.
Simply log in to your account, and you will see the name of the first organisation you've registered at the top left corner. Click on this name, and the dropdown which appears will allow you to 'Add another organisation'. Click here, and your second organisation will be added under your personal account.
If you manage more than one organisation, the email addresses for each organisation are kept entirely separate from one another, and the stories are also kept entirely separate from one another. You may have different team members for each organisation you manage.