What specific challenges do Ralph, Jack, Piggy and Simon face at this point in the novel?

Again, you need to detail your questions. What "point" in the novel are you referring to? 

in chapter 2

The boys need to implement rules, buils a signal fire to alert passing ships and be resuced (as well as keep it burning). They need shelter, food, supervision for the younger boys, a count of exactly how many boys are present on the island, and a fair amount of organization. The boys have their work cut out for them.