This reflects alternate Stewart record denoting Sir John's youngest daughter of his second marriage [to Eleanor Sinclair], Margaret, as the spouse of Robert Robertson, instead of her older sister, Isabel, but this differs with Scots Peerage and the Clan Robertson data.

Origins

John Stewart and Eleanor Sinclair had two sons and nine daughters:

1. John Stewart, 2nd Earl of Atholl, living 1520, and died before 1522, who married Janet Campbell (died about Candlemas 1545/6), daughter of Archibald Campbell, 2nd Earl of Arygll.
2. Andrew Stewart, Bishop of Caithness.
3. Jean (or Janet) Stewart, married by contract dated 31 August 1507, James Arbuthnott of Arbuthnott. He had a crown charter of the feudal barony of Arbuthnott 29 January 1507. He left a testament dated 7 March 1521, and died before 13 March 1521.
4. .Katherine Stewart, married Sir John Forbes, 6th Lord Forbes.
5. Elizabeth/Elspeth Stewart, married Sir Robert Innes 2nd of Innermarky.
6. Marjory Stewart, married Sir Colin Campbell, of Glenorchy.
7. Margaret Stewart, married Sir William Murray, of Castleton who was killed at Battle of Flodden Duke of Atholl
8. Elizabeth Stewart, married Alexander Robertson, of Strowan.
9. Elizabeth (or Isabel) Stewart, married John Stewart, 3rd Earl of Lennox
10. Jean Stewart, married Robert Gordon, Knt., of Pitlurg.
11. Margaret Stewart, married Robert Robertson younger, of Strowan.

From: [http://en.wikipedia.org/wiki/John_Stewart,_1st_Earl_of_Atholl]

References

1. "Red Book of Scotland, Volume 9" (Smi-You). Pages 580-582. < Ancestry.com >; (Document attached). Sir John Stewart, 1st Earl of Atholl, m. firstly, by 25 March 1460, to Margaret, daughter of Archibald Douglas, 5th Earl of Douglas, by whom he was the father of: Janet, married Alexander Gordon; Catherine, married John, 6th Lord Forbes; Elizabeth Stewart, married before 1483, to Andrew, 2nd Lord Gray, (he was widower of Janet, only daughter of Robert, Lord Keith, by whom he had issue. he d. in February of 1514), and had issue. He married secondly, by 19 April 1475, to Eleanora, daughter of William Sinclair, Earl of Orkney and Caithness (she d. on 21 March 1518) .... and by whom he had further issue [2 sons and 9 daughters].
2. https://genealogics.org/getperson.php?personID=I00006027&tree=LEO