There seems to be a lot of confusion on this subject--much of it going back to the first McClure book in 1914 by The Rev. James Alexander McClure. Briefly:
Halbert McClure (d 1754) had a wife named Agnes, but I have never seen any evidence for any of the various maiden names attributed to Agnes. If anyone has any evidence, please post.
Samuel McClure (son of Halbert): had a wife named Mary, but her maiden name is unknown. Kelso represents a misunderstanding of an old letter published in Rev McClure's book.
Moses McClure (son of Halbert): has a proven wife, Isabella Steele, daughter of David Steele. They named their first son David McClure.
Nathaniel McClure (son of Halbert): had a wife named Mary who is usually shown with the maiden name Dryden. That name may be correct, but some serious Dryden genealogists have their doubts. If anyone has developed the evidence, please post it.
Alexander McClure (son of Halbert): had a first wife named SUSANNAH who is usually overlooked, but was his wife by 1753 and the mother of his oldest children. Then, he had a much younger wife, Martha (said to be a Moore) by 1773 who was mother of five of his children. His will is dated 14 Mar 1787, proved Feb 1790. Some of his children were very young when he died.
John McClure (son of Halbert): had a first wife named CATHERINE who is always overlooked, but proven in land records. He probably had no wife named "Mary Malcolm". His oldest children named their eldest daughters, Catherine. Then, ca 1755, John married Mary Allen by whom he had 7 or more children. John McClure was probably older than generally realized. He had surveyed land in old Orange Co., the predecessor of Augusta, in March 1745 which was still owned by his estate in 1778 and sold by his executors. The early records of a John McClure that were once attributed to Halbert's "brother John" probably all belong to this John McClure.
Arthur McClure (POSSIBLE youngest son of Halbert): This Arthur was originally thought to be a son of Halbert's brother, John, but that seems highly unlikely. There is abundant circumstantial evidence that he was a brother to the above sons of Halbert with whom he interacted. His wife was named FRANCES and Rev. McClure speculated that she was a McNabb. Arthur bought his first land from John and Mary McNabb, but I have found no other evidence for the name and "Frances" does not seem to be a McNabb name.
I hope I have not added errors to the ones already in circulation, but I think it is especially helpful to recognize the correct names of the first wives of Alexander and John since they get perpetuated among the descendants.