Merecedes is Hal's sister, she whines, cries, and causes problems throughout. As we see in Chapter 5, she's self-centered. Her presence not only slows the team down but exhausts the animals when she insists upon riding on the sled. Even after the men dump her into the snow, she insists. The dogs can't go on...... she is a selfish MESS.
Hal is young and unthinking. He wants to mine for gold, believing it will make him rich. He too young, too inexperienced, and his purchase of Buck comes at the point that the government has no use for the team. His laziness and misuse of the dogs are proof of his ineptitude.
Charles is completely useless. He follows Hal everywhere (great mentor :-( ). He has a weak constitution, no individuality, and he does what he's told reagrdless if it's right or wrong.
These three characters symbolize the worst side of civilization because their every action is in complete contrast with their desires. They have no work ethic and little sense of values.