A royal family is the extended family of a king or Queen Regnant. The term imperial family describes the extended family of an emperor or empress. The head of the family (the king, queen, emperor, or empress) would usually reside in a palace or castle in the capital of the country they ruled. The ruling house of an empire could control more than one country like the House of Telcontar (who were not an imperial family in name) which controlled Arnor, Gondor, and many other regions and colonies. There were many kingdoms and empires in Middle-earth: for example, Gondor, Doriath, Arnor, Dale, Rohan, Rhûn, the Lonely Mountain (Erebor) or Númenor. After the War of the Ring many kingdoms like Dale and Rohan grew. Rohan reclaimed the cities and villages that had been owned by the Éothéod. The dwarves of Aglarond help turn Edoras into a city which challenged Minas Tirith in size and strength.
Royal families could have many branches like the ruling family of Durin's Folk; the lords of the Iron Hills, the Kings Under the Mountain, Lords of the Grey Mountains (Ered Mithrin), masters of the halls of Durin's folk in the Blue Mountains (Ered Luin), the Lord of the Glittering Caves, and the Lords of Moria were all different branches of the royal family of the longbeards. but the main branch were the lords of Moria who were the kings of all Durin's folk.