How do the guards at the train station react to the death of the Book Thief's brother? What do their responses suggest about the manner in which humans react to sudden death?

The guards argued about the death and what to do. From the text, we can infer that the boys death were nothing more than an inconvenience to the guards.

As you’ve been informed, two guards also exited the train. They discussed and argued over what to do. The situation was unsavory to say the least. It was eventually decided that all three of them should be taken to the next township and left there to sort things out.