According to the "rare old" book given to me by my son Thomas Lackey, titled "Leckie of Leckie" (Leckie of that ilk 1567), by R.G.E.L., published in Vancouver, British Columbia in 1913, John Leckie of that Ilk (1624-1670) was served heir to his father Alexander Leckie of that Ilk in Jan 1648 (John’s mother was Grizel Murray). John had brothers and sisters (Alexander, Euphame, Margaret, Anna, Sarah). John married in 1661 to Jean Buchannan, daughter of Sir George Buchanan of that Ilk and sister to John, the last Buchanan of Buchanan. John and Jean had at least two children, Mary on 12 Jul 1663 and John on 27 Nov 1666. Leckie lost the family lands by two Charles II Royal Charters (Easter Leckie, 12 Jun 1668 and Wester Leckie, 12 Jul 1670).
This book is a well referenced documentary on the descent of the Leckie family, including the Earls of Lennox. The author states that in his researches he came across many references to junior branches of the Leckie family, but to my knowledge he never published those. His book includes appendices on the Lairds of Leckie (but not numbered) and limits family tree history to the main line beginning 965 AD and stops with the "last" Laird of Leckie (John Leckie) in 1670 AD. Among other books of interest referenced are "History of Scotland" by Geo. Buchanan (tranlated by Aikman), 1827 ed, and the County Court Book of Stirling---"The Lairds of Leckie" by W B. Cook.
Your trace down to the eldest male line to the John Leckie (b 1707), 15th of that Ilk (who also married a Jean Buchanan) indicates him to be the GGGrandson of John Leckie (b 1666) unless the count “15th of that Ilk” is wrong? email: firstname.lastname@example.org