Sources: (1) The Laird of Lag, by Alexander Fergusson: book:
Regarding Lag's other children it may be briefly stated that JAMES, his 2nd son, about whom little is known, was at Scots' College at Douay from 1698 to 1700. Shortly before his death he seems to have put in possession by his father of certain lands in the parish of Troqueer. His wife was ELIZABETH FERSUSSON. She survived her husband who died early in 1722 (April, 1721, his will). Their son, ROBERT GRIERSON, already mentioned, in some way incurred the displeasure of old Lag & of William his uncle.
....He was expressly cut off from succeeding to the family estates. This was done by a 4th deed which Lag executed a few days before his death, namely on the 20th December, 1733. In it Robert's name is removed from the series of heirs. It was to no avail that on his uncle's death, he 'took out breaves' and had himself served heir to the estates ; but he could not be excluded from succession to the family title, and he became 3rd Baronet of Lag in 1760, on William's death. So far as I am aware, no mention of him is made in the ordinary books of the Baronetcy.
His sister, HENRIETTA GRIERSON, married JAMES FERGUSSON, Surgeon in Dumfries.
Of Lag's 3rd son, JOHN GRIERSON, little more is known than that he died in 1730. Some of the family details now given for the first time, are established by an Inventory of Writs found in his trunk at his death, on the 16th March, .