Paulo is right - the link between the Cumings of Altyre and the Essex family is certainly fictitious as presented here. Thomas Cuming of Altyre was contracted to marry Margaret Grant, daughter of James Grant of Freuchie, on 15 September 1552, though it's not clear if the marriage actually took place [1]. Either way, he was certainly married to Margaret Gordon, daughter of Alexander Gordon, 1st of Strathdon and granddaughter of the 3rd Earl of Huntly, by 4 July 1561, putting this marriage somewhere in the 1552x1561 window [2].
This in itself makes it clearly impossible for Thomas and Margaret to have had a son born in 1536, but they *did* have a son James and it's worth relating his career as well just to decisively disprove what's shown here. James Cuming of Altyre was his parents' third son but eventually succeeded to the estate. His marriage contract, dated at Elgin, Bog o’ Gight, and Altyre, 29-30 September 1599 and 20 and 26 February 1600, was not with the anonymous Mary named above but with Margaret Gordon, daughter of Sir Thomas Gordon of Cluny [3]. She must have died very soon afterwards as by 16 November 1602 he had remarried to Margaret Fraser, daughter of Hugh Fraser, 5th Lord Fraser of Lovat, by Elizabeth Stewart, daughter of John Stewart, 4th Earl of Atholl [4]. By Margaret he left two children: Robert, who succeeded him, and Jean, who married in 1627 to John Hay of Lochloy [5]. The John Cumming of generation ten is evidently both a generation too old and hundreds of miles further south than this family. To the best of my knowledge, migrations between Elgin and Essex were not exactly standard in this period . . . .
All the best,
Kelsey
[1] Fraser, Chiefs of Grant, iii. 377-378.
[2] Reg. Mag. Sig., 1580-1593, no. 1122.
[3] Reg. Mag. Sig., 1593-1608, no. 1255.
[4] Elizabeth Cumming Bruce, Family Records of the Bruces and the Cumyns (Edinburgh and London, 1870), 465.
[5] Elgin Sasines, 1st ser., iii. 126, 127.