actually upper class, although Mrs. Bennet's more middle class background complicates this status somewhat. 

In any case, one of the ways in which Jane Austen realistically portrays the middle class is by showing how anxious the middle class is to prove its worth to the upper classes. As we all know, Mrs. Bennet (who has married into the upper class, but has a more middle class background) is anxious that her daughters marry and make "good matches." A "good match" would involve marrying a man of considerable fortune and reputation (a man, in other words, from the upper class). By pushing her daughters to marry such men, Mrs. Bennet hopes not only to have her daughters provided for, but also that they will finally be fully accepted into the elite social circle which they are technically already part of, but still somewhat tenuously connected to. In this way, Austen is showing the ways in which people of middle class backgrounds are anxious to be accepted by the snobbish upper class. 

It's worth noting that, in representing this middle class anxiety, Austen's also trying to deconstruct the rigid notions of class in the first place. After all, the middle class characters in the novel are usually presented as financially stable, and even prosperous. However, because their wealth comes from work, rather than inheritance, the elite class persists in rejecting the "newly rich." By illustrating how frivolous this idea is, Austen creates a brilliant, satirical commentary on England's class structure. 

Even though many people feel that Jane Austen is a fluffy writer that doesn't really deal in real problems that humans face, she actually creates quite a bit of real depth in her interactions between people.  She makes the relationships seem very real and relatable in two ways.  First of all, the characters that she creates are very real, meaning, they have flaws and weaknesses just like everyone else does.  Even her protagonists always have weaknesses that they struggle with throughout the course of the book:  Elizabeth was prejudiced, Fanny was overly shy and insecure, and Anne is too submissive and demure.  By giving her characters flaws, that makes them more real.  We like them better as a result, and it also creates more real situations.  Elizabeth's prejudices get in the way of her happiness for a very long time.  So, all of the interactions in the book, between people, are tinged with the characters' flaws, and that makes the dynamics very real.

The second way that the human interactions in the book have realistic tinges is that she portrays both good and bad situations.  Not everyone is married happily ever after.  Not all of the family members love each other without ever fighting or getting annoyed with one another.  Men betray women, and women settle for less than they want.  Every single human interaction, until the inevitable end that has a wonderful wedding and happy-forever feel to it, is filled the flaws that human beings possess.  Austen didn't shy away from relating some of the more negative human situations; people eloped and committed affairs, friends fought bitter battles, families broke and feuded, and scandals were at every corner.  That is like real life.  Real life isn't some happy fantasy land filled with lollipops and rainbows.  Bad things happen.  People get angry with one another.  And Austen did a good job of realistically portraying all of those situations.

I hope that those thoughts help to get you started; good luck!

What makes a novel realistic as opposed to romantic has not to do exclusively with its subject matter, but also with the approach taken to the subject matter. Although the basic plot – that two girls from the lower rungs of the gentry would end up happily marrying rich men – is not entirely probable, Jane Austin eschews the wild imaginative settings and events of the Gothic novel, the preceded her or of the Brontë sisters. Her narration is humourous and matter-of-fact and the character traits her heroes and heroines display are those of normal young men and women of the period. They aren’t geniuses or described as supernaturally beautiful. Elizabeth is clever but not a genius who speaks eight languages and plays the piano as well as a professional (as Mrs. Radcliffe’s heroines often do) and Jane is nice but not a saint.

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