Sometimes, when parents share a common email address, parents will receive duplicate emails for their leave notifications. This occurs because Reach is trying to notify both parents and if their email address is identical, then two emails will be delivered to the same address.

You can prevent the duplication in these instances by turning the communications selector off for one parent in their association with the student.

Go to People Management > Student Profile  and select the Associations tab.  Select one of the parents and set Allow Communications to "No."  Be sure to click "Save Association" and then also save changes to the Contact Details.