It says for me that "Robsten" is a mix of two names. The names would clearly be Robert & Kirsten. Combining both would make the name Robsten... not sure if that's correct, but that's from my knowledge
This metaphor compares their mouth to a desert. This means that either his mouth was too dry to say anything, or that no words would come out of his mouth just as their is not much in a sandy desert.
