I think Sam was the youngest (theoretically, I think David's oldest, then Dan's sister, then Dan and then Sam)

Dan doesn't have a sister. Yes, I know he mentioned one. But, like the Connecticut/New York thing, it's another of Sorkin's screw-ups that he never bothered to catch/correct. The line where Danny mentions a sister was actually supposed to belong to Jeremy, but it got shifted before shooting, and no one caught the error.

Great snippet, btw. You could add the sister into it too. "I had a sister in Connecticut. But by the time I moved to New York, she had inexplicably disappeared."