I have some confussion going on here. I don't have a David McIlwain married to Margaret Davidson. I have:
William McIlwain, son of Samuel and Margaret Kirkpatrick McIlwain, born c1821 in Ireland, married Margaret Davidson, and died March 12, 1896 in Goderich, Huron, Ontario, Canada.
David McIlwain, son of Samuel and Margaret Kirkpatrick McIlwain, born June 16, 1822 in Ireland, married Jane Johnston 1846, and died March 06, 1908 in Goderich, Huron, Ontario, Canada.
David McIlwain, son of David and Jane Johnston McIlwain, born c1865 West Wawanosh, Ontario, Canada, married Annie Elliott September 26, 1894 Colbourne Twp., Ontario Canada.
5534-94 David McILWAIN, 29, farmer, West Wawanosh, Ashfield, s/o David McILWAIN & Jane JOHNSTON, married Annie ELLIOTT, 21, Colborne twp., same, d/o Thomas ELLIOTT & Rebecca BLACK, witn: James ELLIOTT of Colborne twp & Mary McILWAIN of W. Wawanosh, 26 Sept 1894 at Colborne twp.
I don't have your David McIlwain who married Eliza Wilson either. Who were his parents?