i think your thinking of this incorrectly.
people.firstname refers to the firstname column of the people table.
this has nothing to do with the first or second or third join.
it will always ever refer to the firstname column of the people table.
there is no reason to join the application table twice in the sql.
if you have a column in both the people and application table that is named the same, you can refer to them using the table.column syntax:
people.firstname - would return the firstname column from the people table
application.firstname - would return the first name column from the application table.