First you will want to check the spelling of the Users names in Enrollment Management.

If the name is not misspelled navigate to:
  1. Core > Users > Edit User Profile Data
  2. Search for the User
  3. From here you can see what Roles the User has. If they have Past Student and Student (2 of a User Role such as Candidate, Past Candidate, Student, Past Student) then this is why they are being displayed twice.

Let Support know and we will be able to remove the incorrect Role.