I'll define these terms for you and then let you decide which category each of the characters you've named fits into.
A round character is usually the main character or one of the main characters in a story. These characters are fully developed in all aspects: physical, mental, emotional. So they seem to be real people who look, think, and behave the way a real person might (even if the situation might seem unreal, as in science fiction or fantasy). An example of a round character is Huck Finn. You can imagine any teenage boy rafting down the Mississippi.
A flat character is not very developed at all. These are the stereotypes: the villain, the shyster, the knight in shining armor. The author may describe physical appearance in detail but typically doesn't spend much time letting the reader get into the character's head. They are predicable in thought and action. For example, most characters in fairy tales are flat.
A dynamic character experiences some sort of change over the course of the story. That change might be a new understanding or a change of heart or a change in values or commitment. That doesn't include change in physical appearance or circumstance. An example of a dynamic character would be Ebenezer Scrooge, who changes from a miser into a generous person.
A static character remains the same from beginning to end and undergoes no change.
Now that you have these definitions and examples, what kind of characters do you think Daru and the Arab are?