Sunniebraes, near Collessie, is/was in circa 1855 a small house one story high with garden and small farm attached; the property of William Johnston Esq. Lathrisk, and was occupied by David Douglas.

Is David a relative?

I have the following sightly edited correspondence with Peigi from 2012:

If this is correct marriage, Robert Douglas and Mary Black were married 4 jul 1813, Crailing. ...their daughter Elizabeth married Matthew Todd. Matthew and Elizabeth's daughter Susan married Peter Reid; their daughter Mary Wilson Reid, who married George Campbell Ross. Peter and Susan had another daughter, Elizabeth, who married John Lawson and had dau Susan and son Peter, both born in 1890's in Lanarkshire; they later some emigrated to NY in early 1900's (shipfitters).

Robert appears to be the son of a Sholto Douglass and Mary Bruce, married jul 1782 in Auchtermuchty. One of Sholto and Mary's sons is John Douglass, chr 9 mar 1783 Auchtermuchty, married Agnes McAndrew; their son Sholto is the father of the William Sholto Douglas born 1856 Blairgowrie, that went to NZ and became editor of the New Zealand Herald.

Jean, a daughter of Sholto and Mary Bruce, married William Johnston of Lathrisk, son of David Johnston Esq; their marriage is noted in Blackwood's Edinburgh Magazine 1819: "At Edinburgh, William Johnston, squire of Lathrisk and Bavelaw to mistress Jean Douglas, youngest daughter of Mr Sholto Douglas"; as is the birth in 1820, and death in 1828, of their first-born son David. Their second born son George inherited Lathrisk; he died c1903. (If they followed naming conventions, it is possible George was her father Sholto's name as well)

I have no other info on Sholto and Mary Bruce other than their marriage and children. I suspect, but cannot ascertain, a connection with Charles Ayton Douglas's family.

Regarding William Johnstone of Lathrisk, I have the following note:

David Johnston, first of Lathrisk, died before 1810, and his wife in 1819.
The eldest son, David, who recorded Arms, died in 1809 ; the second son,
Captain John, died 1795 ; and the third son, William, succeeded to the
estates. In 1819 he married "Bonnie Jean," daughter of Sholto Douglas,
and their son George was the last Johnston possessor of Lathrisk. On
his death, unmarried, the estates went to Mr Maitland Makgill Crichton, a
descendant of Mary Johnston, daughter of David, first of Lathrisk.