On King Malcolm Canmore’s death, along with his eldest son Edward, at the battle of Alnwick in November 1093 the succession to the throne was thrown into the normal contention between rival claimants. Queen Margaret died three days later. Canmore’s third eldest son from his second marriage, Ethelred, had been made the abbot of Dunkeld to keep this powerful position in the family and was thus not eligible to inherit the throne. Under the laws of primogenitor on one side was Malcolm’s fourth son Edgar from the second marriage. On the other side under the celtic system of tanistry was Malcolm’s brother, Donald Ban. Donald attacked Edinburgh castle and claimed the vacant throne as King Donald III. The remaining four sons from Malcolm’s second marriage (Ethelred, Edgar, Alexander and David) fled to the English Court of King William Rufus. The third claimant to the throne was Duncan, Canmore’s eldest son by his first wife. With military support from England, King Donald was ousted and Duncan was crowned as King Duncan II in May 1094. Six months later, Duncan was murdered and Donald III again reigned. During his short reign, Duncan II gave a charter to the monks of St. Cuthbert that was witnessed by his brother Malcolm and his half brother Edgar.

After Duncan’s death, William Rufus of England preferred to see Edgar on the throne and again intervened. In 1097 Edgar arrived in Scotland backed by another English army and Donald III and his co-ruler and nephew Edmund (Edgar’s older brother) were defeated. Edmund was passed over for betraying his brothers and was allowed to become a monk, but Donald was blinded and imprisoned until his death in 1099.

As part of the ‘Normanization’ of the kingdom, Edgar converted the semi-independent Pictish kingdoms into earldoms under the feudal system. The mormaers became earls with charters for their former kingdoms. King Edgar created the new earldom of Atholl in 1115 and bestowed it upon Madach, the son of his uncle Melmare, youngest brother of his father. On Earl Madach’s death, without a suitable heir, his lands and honors were given by King David I in 1152 to his cousin Malcolm. This Malcolm (second celtic earl of Atholl) was the son of King Duncan II’s younger brother Malcolm from Canmore’s first marriage. The descendants of this Malcolm from Canmore’s first marriage were excluded from the throne in favor of Saint Margaret’s sons but retained the earldom of Atholl.

References:
Bingham, Caroline, "Kings and Queens of Scotland", New York, 1976, pp. 18-20,150.
Fittis, Robert Scott, "Recreations of an Antiquary in Perthshire History and Genealogy", Perth, 1818, pp. 232-233.
Hanley, Cliff, "History of Scotland’, London, 1986, pp. 18-19.
Paton, Sir Noel, "The Descendants of Conan of Glenerochie", privately printed, 1873, p. 3.