My records suggest that Margaret Ann is the daughter of William Polley, Sr. (b. 1812) and Mary Graham (1814-1863). They were married at Petersville, 18 Apr 1838. This connection comes courtesy of a baptismal record for St. John's Anglican Church, Gagetown, dated 30 Jan 1839.
My info on Christopher Graham is more of a stretch. The only person I can link him to definitively is James William Graham (1843-1913), at whose 1868 wedding Christopher was a witness. James was the son of James Sr. and Angelina Emma Graham, so it is possible -- in the absence of any census records prior to 1871 to confirm -- that Christopher and James were brothers.
I hope this helps.