His mother appears to be Isabella SCOTT, daughter of Isabella CADGER who married William OGSTONE....... if the certificates are at least correct in that part, it seems Isabella (SCOTT) and later her son, both used surnames of their fathers - event though both were, each in their turn, illigitimately born.
Alexander PITTENDREIGH - b abt 1848/49
His marriage certificate seems to quite clearly indicate his parents, Alexander PITTENDREIGH & Isabella SCOTT were not married (to each other). Yet he has used his father's surname.
Alexander's death certificate, may be mis-informed that his mother was married PITTENDREIGH ms OGSTON or that his parents were married at all. The inormation seems to be a cobbling of a few separate part truths. Perhaps the informant partially mixed up his mother and his maternal grandmother, or was simply under the false impression that what he/she informed was correct.
It seems that Isabella SCOTT's death certificate is mostly correctly informed - does it say her mother is "CADGER or OGSTON" or does it say "ms OGSTON"? (I can't quite make it out). It appears she also used her father's surname even though her mother was unmarried at the time she was born. The Census seems to indicate, William OGSTON was her stepfather, and CADGER was her mother's (probable) maiden name (probable, because her mother is shown with the CADGER surname in 1841). Wonder who the GORDON laddie is though....
http://www.freecen.org.uk/cgi/search.pl1841: Whitewell, Tyrie, Aberdeenshire
William OGSTONE 60,
Isabel CADGER 33,
Isabel SCOTT 13,
James GORDON 12,
William OGSTONE 6,
John OGSTONE 3,
Elizabeth OGSTONE 8 mths,
Elizabeth FRASER 53, Female Servant,
ALL Born Aberdeenshire
http://www.freecen.org.uk/cgi/search.pl1851: Whytewell, Tyrie, Aberdeenshire
Head: William OGSTON 80, Crofter& Butcher, b Tyrie
Wife: Isabella OGSTON 45, b Fraserburgh
DauLaw: Isabella SCOTT 21, Farm Servant, b Strichen, Aberdeenshire
Dau: Elizabeth OGSTON 10, b Tyrie
Son: Robert OGSTON 8, b Tyrie
Dau: Joan OGSTON 4, b Tyrie
Son: Charles OGSTON 3, b Tyrie
Dau; Barbara OGSTON 6, b Tyrie
1861: Milltown Boyndlie, Tyrie - in Household of William FOWLIE, Parochioal Schoolamster & Farmer 50 acres
Servant: Charles OGSTON 12, Cattle Boy, b Tyrie
Servant: Alexander PETTERBRIGH??, 9, b Tyrie
1871: Alexander PITINDREICH 20, b Tyrie
Farm Servant at Mains Of Auchnagatt, New Deer (Savoch)
BIRTHS IGI: At Tyrie, to parents: William OGSTON & Isabella CADGER
William OGSTON b 19 Jun 1834
John OGSTON b 7 May 1838
Elizabeth OGSTON b 13 Oct 1840
Robert OGSTON b 13 Jan 1842
Barbara OGSTON b 13 Mar 1843
Joanna OGSTON b 18 Dec 1845
Charles OGSTON b 2 Nov 1848
Cheers
AMBLY