It may just be a coincidence but there are too many common factors here to ignore the possibility that John and/or Margaret are related to James and Sarah.
John McGee was born
Margaret Dunigan was born
before 1830
John and Margaret had the following children (that I know of) —
CHILD born in YEAR in PLACE , last sighting 1911.
1830 Thomas McGee was born on Sunday, June 20.
From the Register of Baptisms in the parish of St. Andrew's, Glasgow —
“Thomas, lawful son of John McGee and Margt Dunnigan, born on the 20th ult, was baptised by me on the 4th July, 1830. Sponsors were Henry Dunnigan and Sarah Dunnigan. Charles Grant.”
Also baptised on the same day was Catherine, daughter of Henry Dunigan and Mary Smith with sponsors John McGee and Agnes Dunigan.
1832 Elizabeth McGie was born on Thursday, April 12.
“Elizabeth lawful Daughter of John McGie and Margt Dunnigan, born on the 12th March, 1882, was baptised by me on the 22nd April, 1832. Sponsors Bernard and Elizabeth Dunnigan. William Gordon.”
1841 June 6 Nothing obvious (based on Thomas) in Lanarkshire (including Glasgow).
1851 March 30