Difficult Passage of Heart of Darkness

I was not quite sure about the passage at the beginning of Part II on pages 102-104 of Heart of Darkness. The nephew and the uncle are talking and gossiping about the events of the station. Who are the nephew and uncle? Also who are they discussing in this quote: "Who was it they were talking about now? I gathered in snatches that this was some man supposed to be in Kurtz's district and  of whom the manager did not approve." Are they talking about Marlow or some other random European man in the Congo? What is the purpose of the Conrad including this scene. Why is it important for Marlow to overhear the uncle and his nephew?