When two parent/guardian details are added to a form, the email address for each needs to be unique. The form will show an error if the same email is used:
There may also be instances where the parents will share an email address.
To bypass the error, parents can add "+1" just before the "@" symbol in the email address, and the form will accept this as a different address. However, you must keep in mind that when an email is sent it will go to the main address twice.
For example, if their email address is firstname.lastname@example.org then they can use email@example.com and the "+1" will be ignored, meaning they will receive the email to firstname.lastname@example.org