multiple customers

HELP!!!

I have a situation I am trying to decide what to do. 

currently have Tables

Customer
Contact
Opportunity
Opportunity Contact selection

Customer is parent to Contact
Contact is parent to Opportunity Contact Selection
Opportunity is parent to Opportunity  Contact Selection. 
Thus making Opportunity Contact selection table linked or many to many table

In my Opportunity table I have a customer field.  I would like to be able to put a customer #2 field in that I can pull another customer.  ie.  Main customer and secondary customer because sometimes we do work for a municipality directly and sometimes we do work for the municipality but it is under a General Contractor (or engineering firm)  where the General Contractor would be our customer.   I would also then like to be able to select contacts from either one of the customers. ​


Can this be done and how?

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Tina Revermann
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