The base unit of any poly configuration is Individuals. Not couples, or dyads or triads or what have you, Individuals. Two individuals interact in some dynamic, this is their relationship to each other, whatever form or style that relationship takes (neighbor, co-worker, acquaintance, friend, intimate, partner). Two individuals can form a couple or a dyad. Three individuals can form more relationship connections in different forms, i.e. a triad or a V. Any network or polycule (or however you want to describe a group dynamic), is made up of multiple individuals with multiple relationships.
It makes me a little crazy dealing with people who think somehow that poly is matter of couple+. These are the kind of people who discuss everything as "WE". As though the only way to be poly is to start as a monogamous couple and then deign to "allow" other people into "their" relationship. Its kind of insane, really. If you are in a relationship with someone there are two individuals involved, if there are more people then there are more individual dynamics/relationships. New people are not added to your existing relationship. Yes, new people and new relationships can affect your existing relationships, just as new people moving into a residence can affect the environment. But your relationship to one person is never the essential part of that persons relationship to someone else. I'm sorry, but it doesn't work that way, the world does not actually revolve around you or even around the two of you as a conglomeration.