I have slightly different information from yours, so just to add to the confusion:
I have Matilda's mother as a "Kilpatrick", not a "Kirkpatrick" (from her Death Certrificate).This seems to fit with others around at that time. The informant was her second son, Thomas Gordon.
Rev Cunningham Atchison was married to Isabella Osborne (daughter of Dr John Osborne and Mary Clark from Lifford)and was the son of Robert Atchison and Catherine Kilpatrick. I have seen the record of the Marriage Certificate, and this is confirmed through death certificates and the book "Illawarra Pioneers".Cunningham never resided in Bathurst, but his brother Samuel (c1809-1847) did.Cunningham came out with Rev John Dunmore land on the Portland in 1837, and was in Parramatta 1838-41, Wollongong 1841-64 and Sydney 1864-70, dying on November 7 1870. There is a street in Wollongong which I presume is named after him.
Samuel's relative Catherine (sister or daughter, not sure) married David Warnock, but I have no further information.The reception of Catherine Purvines 1847 marriage to Alexander Crilly was held in the home of Samuel and Rebecca Atchison in Bathurst, and Samuel and Catherine were witnesses to the 1846 marriage of Anne Jane Purvines to James Maher (reputedly a former convict!), so the families must have been close.Alexander emigrated on a ship, the "Moffatt" in 1841 with a few Atchisons and Samuel & Rebecca were on the "Coromandel" with Anne Jane and Catherine Purvines in 1840.
The information on David Gordon's death certificate states that his mother was, as you indicate, Matilda Curpatrick, but his immigration records into Australia give his mother's name as "Anne".His death certificate information was provided by his youngest son, James Stewart Gordon, whereas David himself provided his immigration information. I have no other evidence either way.
I have another son, who you may not know:James MacDonald Gordon, born 6 May 1987.
Thanks for your information - hope I have helped, not hindered!