Only Sam, Jane, and Callie have middle names. Jane's full name is Lady Jane Grey. I'm not sure if Jane or Grey is her middle name. I call her Jane or "li'l girl".
Sam's full name is Samwise Rory Beauregard Gamgee, the Red. I call him Sam.
Callie's full name is Calla Lily. Sometimes she is called Callie, sometimes Lily.