In one Production Box many(7) Databases running....and when I run ps -ef|grep pmon, 2 pmon entries found for the same database.....

oracle 12656 1 0 May 25 ? 12:26 ora_pmon_usarpt
oracle 8481 1 0 Jul 2 ? 0:30 ora_pmon_usarpt

checked alert log and found someone(I am new to this envirnment) tried to open already running database by mentioning different pfile option...so I guess 2nd instance is running too.....

Can anyone tell me what is the best/safest method to shut down the second instance without affecting the production DB....my fear is I should not shut down the production thing....

Not much found in metalink/google etc on this.....