Socially the Bennets belong to the landed gentry class. Mr. Bennet is a gentleman farmer of moderate means whose main source of income is from his estate:
Mr. Bennet's property consisted almost entirely in an estate of two thousand a year. [Ch.2]
The Lucases are socially inferior to the Bennets because they belong to the trading class:
Sir Willaim Lucas had been formerly in trade in Meryton. [Ch.5]
In Jane Austen's time ownership of land was the single most important indicator of social status. It was not the amount of money you had but the amount of land you owned which determined your social status. For instance, Darcy the hero of the novel owns a large estate at Pemberley and in Ch.56 his aunt Lady Catherine comes to Longbourn to dissuade Elizabeth from marrying him by hinting that Elizabeth belongs to a different social class than Darcy's. Elizabeth at once angrily retorts,
He is a gentleman; I am a gentleman's daughter; so far we are equal.
In Ch.5 we read how Sir William Lucas attempted to gloss over and disguise his socially inferior status:
Sir William Lucas had been formerly in trade in Meryton, where he had made a tolerable fortune and risen to the honour of knighthood by an address to the King during his mayoralty. The distinction had perhaps been felt too strongly. It had given him a disgust to his business and to his residence in a small market town; and quitting them both, he had removed with his family to a house about a mile from Meryton, denominated from that period Lucas Lodge, where he could think with pleasure of his own importance, and, unshackled by business, occupy himself solely in being civil to all the world.
Although the Bennets and the Lucases belong to two different social classes they are good friends, especially Elizabeth Bennet and Charlotte Lucas and both the families face the same problems -- limited sources of income and the marriage of the daughters.
Both Elizabeth and Charlotte have diametrically opposed views to marriage. In Ch.22 to Elizabeth's shock and surprise after Charlotte has accepted Collins' marriage proposal, Charlotte defends herself by remarking,
I am not romantic, you know. I never was. I ask only a comfortable home; and considering Mr.Collins' character, connections, and situation in life, I am convinced that my chance of happiness with him is as fair as most people can boast on entering the marriage state.''
Elizabeth unlike Charlotte is "a rational creature" who strikes the right balance between 'romance' and 'realism.' In Ch.19 she angrily rejects Collins' proposal saying,
Do not consider me now as an elegant female intending to plague you, but as a rational creature speaking the truth from her heart.
Elizabeth Bennet courageously rejects the marriage offer of Collins who will inherit her father's estate because her father has no male heir. After her father's death she, her mother and her sisters will have to vacate the house. Elizabeth could have prevented this by agreeing to get married to Collins. By refusing to do so Elizabeth proves her strength of character. She is rewarded at the end of the novel for her strength of conviction by getting married to Darcy the wealthiest man in the whole novel with a large estate with an annual income of ten thousand pounds.
Interestingly, readers see little of the families gathered. The beginning of the novel includes the scene where the Bennets are discussing meeting Mr. Bingley. Readers realize that this is a family where the parents have little in common except their children, not uncommon in that time, and that they have little respect or affection for one another. The parents have their favorites. The Lucases readers never see gathered and having a family discussion so inferences are unbalanced.
Social status and economic status are apparent. The Bennets do not have a son to inherit, but the Lucases might ("younger Lucases" I believe is how the younger children of unmentioned gender are called). Though the Lucases are a family of the minor gentry, the title is insignificant since Sir William Lucas is the first to bear it. No mention is made of any connections until Charlotte marries Mr. Collins. Additionally, Bingley's sisters note with disdain that he had presumably been a shopkeeper. The family lives in the country and does not participate in London society. They live simply, and the daughters help around the house, which Mrs. Bennet reveals. The Bennets attempt to live better in keeping servants and a cook. Their girls are left to their own devices and given few formal skills. Mr. Bennet has inherited Longbourne, and it appears to have been in the family for a few generations since the entailment exists. When the patriarchs of these families die, the widows and unmarried daughters will have little to live on but the generosity of others. For the given time, the Lucases are the "better family", and if they have a son, they are a more financially stable family.
Following the marriages of Charlotte, Jane, and Elizabeth; the relative social and economic status of the families changes. Elizabeth and the Bennets are now connected to Lady de Bourgh, being Darcy's aunt. This is a better connection than the Lucases have with Charlotte married to the minister Mr. Collins whose patroness is Lady de Bourgh. The Bennet daughters still lack titles; however, their connections to men of income, property, and titled connections is greater than that of the Lucases at the end of the novel.