This section does a great job of setting up both the time/place of the action and the many characters that will be living in it and taking part in the mystery. Sixteen characters are a lot to juggle, especially in a shorter novel, and Raskin does a great job of providing a little bit of detail on each of them while also advancing the plot.
The idea of putting up a bunch of people to compete with one another to win a heck of a lot of money sets up a perfect, textbook conflict. There are eight teams of two and each of them wants to win the inheritance. It's husbands against wives, children against parents, and old enemies against high school students, as the group of sixteen works separately to figure out a prize that none of them are able to solve on their own.
There are sixteen people playing the game, and each of them encounters one complication. One sets off bombs, one hires a PI, three go to the hospital, and just about all of them spy on each other. During all this, we learn more about each of the characters, what their "real" identities are, and what some of them wish their real selves could actually turn out to be.
The heirs gather together to hear the last part of the will read; several teams are convinced they have the right answer, while other teams despair that they have no answer at all. What's interesting is that several teams' answers point to one character, Otis Amber, and none of them put him forward as the solution. Everyone's disappointed when the answer seems to be "Berthe Erica Crow," and Crow puts herself forward as the answer, while Sandy dies and the others find out that they seem to have lost the game.
In a trial-like scene, the remaining characters gather to go over the will, kind of like they did in the "Conflict" stage. This time, they go back over each of the details in the will, pausing to ask each other questions and try to find out what Westing meant. While everyone else seems to think the game is over, Turtle realizes it may not be, and races against the clock to figure out the answer without letting anyone else know she's onto something.
You'll notice that in the section "What's Up With the Ending?" we called this moment the first ending, even though it can also be seen as the denouement. This is because it's a way of figuring out the main problem at the heart of the story and putting the characters back in their places, but as such it also seems that the "solution" would be a kind of ending to the mystery. Anyway, Turtle figures out the puzzle, but nobody else does; the rest of the characters manage to content themselves with their shares in Sunset Towers and look toward the future.
The two conclusion sections take two jumps forward in time: first, five years later, and second, about fifteen years after that. At each of these moments, the text reveals a rapid rundown of what's happened in or to each character's life, kind of like showing us a photo album at a high school reunion. We get closure on each of the characters, and watch as the prize that was won by Turtle during the denouement is finally and fully awarded.