I was flipping through the Personality chapter, and noticed that it was the one that had information about the twin studies. They really are a very interesting read. Some of the coincidences are almost crazily similar in fashion, such as the two brothers who were separated, became very strong and politically active, and then discovered that one was a Jew and the other was a Nazi in the Hitler Youth movement. It seems like it has a large impact on the nature vs. nurture debate. We see that while they possess many of the same characteristics that they would have no matter where they grew up, the environment they grow up in and the values of those around them can also contribute greatly to choices that they make later in life. Another set of twins was discovered to both have grown up and become firefighters, one in New Jersey and the other in Queens, New York. Although much of the could be seen as coincidence, many studies done have produced similar results.
Cody Morin - Chapter 14
In the twin study where one twin became a Nazi and the other was Jewish, while they different outlooks they had very similar personalities. They were highly loyal to their cause and strong willed.
Twin studies are indeed fascinating. Some of the examples, like the ones you mentioned, are crazy. It is great that we are able to utilize twin studies to learn a lot about psychology.