ROYALTY The royal family in England has always been the Black family. However, due to familial connections, the bloodline extends much further than a single line. Bellatrix and Narcissa, nieces to the king, have married into respectable pureblood families, making them eligible for the crown. The Longbottoms, while the line has been long since diluted, remain pillars of society and ever present in the palace, causing many to consider them royalty as well.
Only the Blacks, however, are referred to as princes and princesses. The Lestranges, Malfoys and Longbottoms are not included withing the royal ranks and are considered Dukes and Duchesses. The younger generation are Lords and Ladies.
HIGH NOBILITY The High Nobility are made up of mostly pureblood families, although lines have been diluted in recent years. These families have diplomatic jobs within the United Kingdom to assist the crown. Each family either works as treasurers, law enforcement, or courts in their specified areas.
The teasurers are the Shafiq family in Wales and Ireland, the Edgecombe family in Scotland, and the Longbottom family in England. The head of law enforcement are the Patil family in Wales and Ireland, the Crouch family in Scotland, and the Lestrange in England. Those in charge of the courts are the Parkinson family in Wales and Ireland, the Greengrass family in Scotland, and the Potter family in England. The Rosiers assist the crown abroad as ambassadors.
NOBILITY The nobility is made up of mostly pureblood families in good standing with the crown. However, nobles are anyone who has been officially recognized by the crown for a service performed. Not every pureblood is nobility either and nobles can certainly be demoted for any reason the king deems necessary. It is common for bodyguards to be promoted to noble status for saving the life of a member of the royal family, as are exceptionally talented Quidditch stars and Triwizard Tournament champions.
Nobles are often invited to the palace for dinner parties and to witness royal events. They are of the highest standing in society without being royalty themselves and have the most rights.
Unlike in Muggle British royalty, the nobility here do not have titles, as those are allocated to only the royalty and high nobility.
KNIGHTS/SERVANTS These are the people who work for the crown. They were all commoners before, but in deciding to serve the crown, their status has been elevated. There are two different ways to serve the crown.
As a knight, everyone is expected to protect the royals in different ways. Bodyguards, secret agents, aurors, etc. Every knight is sworn to secrecy on their knowledge of what goes on in the palace and are allowed to live among the nobility. They are still second-class citizens, but they are treated much better because they are instrumental to the success of the kingdom.
Servants are those who clean the palace, cook the food, set up for events, etc. The servants serve the crown in every way that doesn't include protection. Servants are second-class citizens, but many live in the servant wings of the palace. They are allowed to leave in their off time, but they have specific quarters and don't have to pay for lodgings or food.
COMMONERS These are the third-class citizens of the country. They are the people who work outside of the palace and aren't considered purebloods. Being a commoner does not mean the individual is poor, but they are not given as many perks as the nobility. They aren't invited to the palace. They aren't treated so poorly that they have to live in squalor, but they are certainly looked down upon by the upper class.
REBELS The rebels can be from any social class. These are the people that feel society needs a change. They are underground and, technically, they are not a social class. If they were caught rebelling against the crown, however, they would be given harsh punishments, regardless of social status. Royalty, nobility and commoners are all treated the same when placed in prison for treason.