Contact Groups with Parent / Partner companies

I am trying to find a good method to improve which contacts receive which kind of email from us in a fast and easily update-able way.  So, whether it be accounting related, shipping related, scheduling related, I should be able to manage the type of emails that the contact receives.  This would be fairly easy with some custom checkboxes and dynamic groups (eg a box that says "Receive Accounting Emails" and a saved search based on that)....

However, there is some added complexity.  Some contacts in a parent company should receive emails relating to several subcustomers.  So, person A belonging to Parent Company B needs to receive accounting emails for Subcustomers C, D, and E, but not for F, G, or H.  There are also instances where one subcustomer should get an email relating to another subcustomer.