How can I link 2 accounts to an opportunity?

Summary:

I have created a Dynamic Choice List type field in the Opportunities object that queries the accounts object for one type of accounts, but I need that Opportunity to be related to both accounts.

For example: I have an Opportunity where I select from the Account field a type A account, but in the other DCL field I select type B accounts. When I enter the account type A I can see the relationship of the opportunity to the account but not in the account type B because it was only selected in the opportunity.

What adjustment can I make so that the opportunity can be related to both accounts?