Display one row over another if there are two
Wrap your query in a common table expression and add a row number column like this

SELECT DISTINCT
  Employees.ID, 
  Employees.FName,
  Employees.LName,
  Address.City,
  Address.State,
  Site.ID,
Row_Number() over(partition by Employees.ID order by Site.id) as rn


Then, select from the common table expression where rn = 1