A few more records which could be relevant:

I suspect that this is the IGI’s version of the marriage of Thomas Costain, but that there may have been some mistranscription eg his age. And the name of his mother----Mary could be his stepmother ? The IGI has a marriage in 1855 in Gore District, Ontario, of a John Caston and a Mary Ann Neil which may be significant (it could be Mary Ann Kneale ?).

Name: Thomas D Costin
Event Type: Marriage
Event Date: 31 Mar 1870
Event Place: Burford, Oxford, Ontario, Canada
Age: 33
Birth Year (Estimated): 1837
Father's Name: John Costin
Mother's Name: Mary Costin
Spouse's Name: Alice A Read
Spouse's Age: 20
Spouse's Birth Year (Estimated): 1850
Spouse's Father's Name: Charles Read
Spouse's Mother's Name: Hannah Read

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Death of a younger brother of Thomas Darcy Costin:

Name: John Costin
Event Type: Death
Event Date: 14 Oct 1912
Event Place: Brantford, Brant, Ontario
Gender: Male
Age: 62
Birth Year (Estimated): 1850
Father's Name: John Costin
Mother's Name: Ann Duke

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This looks like the Costin family in 1861:

Name: John Costin
Event Type: Census
Event Date: 1861
Event Place: East Oxford, Oxford, Ontario, Canada
Enumeration District: 01
Gender: Male
Age: 41
Marital Status: Married
Religion: C Of England
Birthplace: England
Birth Year (Estimated): 1820
Sheet Number: 15
Affiliate Film Number: C-1061-1062

Line Number: 30
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Name: Mary A Costin
Event Type: Census
Event Date: 1861
Event Place: East Oxford, Oxford, Ontario, Canada
Enumeration District: 01
Gender: Female
Age: 60
Marital Status: Married
Religion: W Methodist
Birthplace: England
Birth Year (Estimated): 1801
Sheet Number: 15
Affiliate Film Number: C-1061-1062

Line Number: 31
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Name: John Costin
Event Type: Census
Event Date: 1861
Event Place: East Oxford, Oxford, Ontario, Canada
Enumeration District: 01
Gender: Male
Age: 10
Marital Status: Single
Religion: W Methodist
Birthplace: England
Birth Year (Estimated): 1851
Sheet Number: 15
Affiliate Film Number: C-1061-1062

Line Number: 36
**********

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Could this be the death of the second wife of John Costin b 1819 (whose first wife was Ann Duke) ?

Name: Mary Ann Costain
Event Type: Death
Event Date: 23 Sep 1893
Event Place: East Oxford, Oxford, Ontario
Gender: Female
Age: 90
Birthplace: Isle Of Man
Birth Year (Estimated): 1803

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Could this be the 1881 census entry for widowed second wife of John Costain b 1819 and this Kneale family ?

Name: Mary Ann Costin
Gender: Female
Age: 75y
Birth Year: 1806
Birthplace: England
Marital Status: Widowed
Ethnicity: English
Religion: Meth. C.C.
Head of Household Name: Thomas Kneal
Event Place: Oxford East, Oxford South, Ontario, Canada
District Number: 165
Sub-District: F
Division: 1
Page Number: 24
Family Number: 119
Affiliate Film Number: C-13267
Household Role Gender Age Birthplace
Thomas Kneal M 58y Ontario
Diana Kneal F 32y Ontario
Jeanette Kneal F 10y Ontario
Mary Kneal F 5y Ontario
Annie Kneal F 5y Ontario
Matthew Kneal M 3m Ontario
Mary Ann Costin F 75y England
Isabella Blair F 15y Ontario

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1891 Canada census:

Name: Mary Costin
Gender: Female
Age: 89
Birth Year (Estimated): 1802
Birthplace: Isle Of Man
Marital Status: Widowed
Religion: Methodist
Province: Ontario
District: Oxford South
District Number: 105
Sub-District: Oxford East

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And now I’ve discovered Morag’s tree on Ancestry which has all of this and lots more. Here’s the link:

www.trees.ancestry.co.uk/tree/8527307/person/-447504583

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Mary Ann was Mary Ann nee Kinrade. She was the widow of Hugh Kneale when she married widower John Costain. Thomas Kneale age 58 in the 1881 census above was her son.

Jean