Mandy N mentioned below that she saw some similarities between Olivia and Sophia and Elinor and Marianne. I had noticed this too, while reading, and wanted to expand on this thought a bit. I think there will be more to write about later, as well.

In this case the eldest daughter, Olivia, is the one who resembles Marianne in some ways. Her beauty is more striking and she seems more vivacious (although Marianne is not really vivacious) while Sophia, like Elinor, is quieter and more thoughtful.

The similarities are more evident with their encounters with men. Squire Thornhill, like Willoughby, has a reputation with the ladies and apparently there is "no virtue able to resist his arts". Although Marianne is not aware of this aspect of Willoughby's character when they meet, her beahviour the first time Willoughby is invited to their home is very like Olivia's with Thornhill's first invited visit.

I was particularly struck by this line: "An age could not have made them better acquainted" (Ch. 5 p. 28 of my book) This is so like Marianne and Willoughby in Ch. 10 of S&S