What do I do if when signing up a patient their email already exists in the database?
First, I would exit the signup and make sure the patient is not already signed up. We don't want anyone to be double-billed. In the case that a couple, or a family would like to receive email notification for both accounts to the same email, you can use one email normally on the first account, then on the second account re-format the email as follows.
For example: jonah@boomcloud.com -> jonah+123@boomcloud.com
The system will see the characters between the "+" symbol and the "@" symbol as void, and send the emails to the same place.