Actually, Britain has had several Royal families in the past 1,000 years.
The current queen was born a member of the Saxe-Coburg-Gotha family, which changed their name in World War One to Windsor. Saxe-Coburg-Gotha was a minor German state. Queen Victoria’s consort, Albert, was a member of this family.
Before that, you had the Hanoverians, who controlled the German state of Hanover (they were Kings of Great Britain and Kings of Hanover at the same time). They came in because the House of Orange, from the Netherlands, became extinct with Queen Anne dying childless. The Hanoverians were the closest relatives to the House of Orange.
The House of Orange was brought in to replace the Stuarts when they were over-thrown by Parliament. Parliament feared that the Stuarts were going to reinstate Catholicism as the state religion. This also set up 2 major rebellions, in 1715 and 1745, when members of the Stuart family were finally defeated.
The Stuarts replaced the Tudors when Queen Elizabeth I died childless. The Habsburgs of Spain actually had a better claim to the throne, but a union with Catholic Spain wouldn’t fly politically so the Stuarts of Scotland were chosen instead. This also had the effect of joining the English and Scottish crowns.
The Tudors were a cadet branch of the Plantagenet family, as were the Lancastrians and Yorkists, who fought over the crown in the 1400’s. The Plantagenets were originally Counts of Anjou, in France, from about 900 CE onwards, and gained the English throne through a marriage to William the Conqueror’s grand-daughter.
Before that, you had the House of Normandy, who conquered England in 1066, after Edward the Confessor of the House of Essex died childless. The House of Denmark also ruled England for awhile, about 1,000 years ago.