I'll be willing to offer some help, but I'll leave it up to you to complete the assignment.
One possible question might be "How did you choose leaders?", then have each of them respond by discussing how the boys initially elected who would be in charge.
Another relevant question you could ask is "When did things start to go wrong?"-perhaps Ralph and Jack would have different responses to this one. Jack wanted to hunt and have fun while Ralph focused on order and getting rescued.
Other important questions could be "How did you feel when Piggy and Simon were killed?", "How did the younger kids act and survive on the island?", "Did you ever think you would get rescued?", and "How do you feel about your stay on the island now?"
There's also a link to the enotes chapter summaries of the novel.