Tirian calls the chief Calormene a “miscreant.”  What does that mean?   

That means the person who behaves criminally and viciously. The Calormene treated the Dwarfs badly to push them to work in the mines of the Tisroc and called them dogs. So Tirian was so angry to call the chief soldier as “miscreant”

What does the Black Dwarf’s name make you think of?  Does the name seem to fit his temperament

I’m not sure if the “Griffle” is really suitable for his temperament. But the Black Dwarf was skeptical for the existence of Aslan. They had no faith in Aslan. Besides, He didn’t show any grateful when dwarfs were rescued by Tirian and Children.

How is Tirian surprised by the dwarfs?  Whom do the dwarfs say they are for?  

When they rescued the dwarfs from Calormene soldiers, he thought the dwarfs to help him to fight with the enemies, but the little beasts were not glad. The dwarfs said they didn’t believe any stories about Aslan and they won’t fight with Tirian because they thought that Tirian just wants to make use of them to fight. Yes, Tirian had never dreamed that one of the results of an Ape’s setting up a false Aslan would be to stop people from believing in the real one. So Tirian was surprised by the dwarfs’ thoughts and behaviors.

The dwarfs said “ the dwarfs are for the Dwarfs”, they won’t believe Aslan, kings or any stories about the other world. They will do for themselves.