Oracle Script For Getting Long Active Sessions
Presumably they are active and doing things so looks like you might need to get more info about your sessions before killing them off. I usually use a query like this to get important info about active sessions including how long they have been logged on (oldest at top), and also how long they have been running the current SQL. 

SELECT USERNAME, 
       TERMINAL, 
       PROGRAM, 
       SQL_ID, 
       LOGON_TIME, 
       ROUND((SYSDATE-LOGON_TIME)*(24*60),1) as MINUTES_LOGGED_ON, 
       ROUND(LAST_CALL_ET/60,1) as Minutes_FOR_CURRENT_SQL  
  From v$session 
 WHERE STATUS='ACTIVE' 
   AND USERNAME IS NOT NULL
ORDER BY MINUTES_LOGGED_ON DESC;