Surely you would know by the Tweets on the account which account is the business one?
Change the password on the account you are signed into at the moment, note the new password then log off,
Go onto the other account which you can find by doing a search for the business name (which you said you had done and saw the tweets). Go to log in and press the 'forgot password' link. When it asks you to put in the email address start trying all the different addresses you can think you maybe used. Twitter will tell you if there is an account associated with that email. Once you've found the email continue with the forgot password link.
Phew I need a lie down ;-)