[Hawkeye]

On the list of employees you can just hover over the bottom right corner of the table and drag it down to as many employees as you want.

The Employee data validation on the Calendar view tab is a named rage (lstEmployees) so it references the entire table column by default which you can see in the Formulas > Name Manager. There is nothing additional you should need to do aside from expanding the table and filling it in.

Edit: If you want to be able to check the formulas you can click in them to see what the main functions are, colored names are named ranges (mentioned above) and the other bits are TableName[TableColumnName] which are treated as an array of values from the referenced table and column.