how can you say that the two boys were willing workers?
why did the two boys hate germans?

Both the boys were willing to do any kind of work that came their way. They did different kind of things like selling fruits, polishing shoes, running errands and even acting as guides. This shows us that they were willing workers. They hated the Germans because it was due to them that their father was killed and their house was destroyed. Their whole life was destroyed and they were left homeless on account of the German war.