there isn’t a single person on board. It is possible because the boat is filled with people, who are not single. It denotes the marital status of everyone. So the people who all are present in the boat are not single; they are married.
The House is an example of symbolism. By trying to hide the dead body of the old man from the policemen under the floorboard. The narrator is symbolically trying to hide the guilt and shame of his crime in his subconscious.
