The Doone family in the novel is based on a real family of outlaws and murderers that lived on Exmoor at the time. A detailed account of the origins of the Doones has been provided by Ms Ida M. Browne, who is apparently a descendant of the Doones of Exmoor.
In 1580 Elizabeth, Countess of Moray, married Sir James Stuart of Doune. Sir James had a twin brother, Ensor. Constant friction existed between the brothers as to the legal ownership of the title and estates of Doune Castle, situated near Stirling in Perthshire.
In 1602, Sir James was murdered by his hereditary enemy, the Earl of Huntley. The Earl was a friend of Ensor, and it was commonly supposed that Ensor had paid the impoverished Huntley to assassinate his brother. James, 2nd Earl of Moray, succeeded his murdered father.
In 1618, Ensor’s son Ensor James Stuart assumed the surname of Doune. This was viewed by his cousin, the 2nd Earl of Moray, as a claim on Doune Castle. The Earl gave Sir Ensor and his wife the choice of exile or imprisonment. They left Scotland and travelled to London, where they sought an audience with the King, which they never received. Subsequently, they made their way to Exmoor, where they raised their sons as robbers and murderers. For 73 years they terrorized the area. In 1699, a new Earl of Moray invited them to return to Scotland, which they did.
There is some dispute as to the validity of this account, although many historians have accepted the truth of Ms Browne's version. Whatever the precise details, there is strong support for the theory that the Doones were a real family of outlaws, of Scottish origin, living in the Exmoor area during this time.
Ida Browne’s full account of their history can be read here.