Yes it looks like your wife and I are distant relatives. Quite amazing how fairly easy it is to bump in to distant relatives thanks to internet connections!
I know very little about the Langlands and Sturrocks, I happened across them while concentrating on my Phillip line.
All I know of Agnes Fairweather, my gggg grandmother is that she was born 3 May 1782 Rescobie, and died 6 Jun 1859 at Friockheim. She married Alexander Meffan at Inverkeilor 21 July 1804.
Of Martha's daughter, Susan Sturrock, I know she was born May 1837 Guthrie, and married my ggg uncle James Phillip on 23 Dec 1864 Guthrie. Their children included: William Sturrock P(hillip), Betsy Meffan P, Isabella P, James P, Thomas P, Andrew P, Margaret P, Georgina P and Eliza P.
Would be delighted to learn more if you are able to help.