Who are the comptroller of those individuals?
SELECT Comptroller FROM PARTY WHERE US_Senate in  ( SELECT US_Senate FROM PARTY WHERE PARTY IN  ( SELECT Party FROM party GROUP BY Party HAVING COUNT ( * )    > =    2 )  ) 
comptroller of those individuals refers to the role 'Comptroller' associated with parties or individuals; individuals belonging to parties with at least 2 members refers to using a GROUP BY and HAVING COUNT(*) >= 2 clause to filter parties with two or more members;