If it is a foreign key relationship with the dreamfactory user table, you can query your table with the related attribute pointing to user table. That will bring back user details in the same response. Have you tried that?
In the API Docs, try putting a * (asterisk) in the "related" attribute and see the response. Now, pickup the relationship name and place that instead of the * to get only the related table information.
Let me know if that does not work.