Brothers from one family marrying sisters from another family is not an unknown event for this region of Southwestern Ontario, even in my lifetime. Finding primary documents that provide hard evidence from the Western District of Upper Canada (that is to say before 1851) is another story.
The Western District up to 1851(1) contained today’s counties of Essex, Kent, Lambton, and Huron. The two families originally were from the township of Zone (here we have some primary data, a lot of secondary references, and even more conjecture). Zone township was divided when the county system was organized in 1848. Part of the township was included in Kent County, and part in Lambton County. By 1851 the creation of county courthouses meant that there is a more complete collection of civil records available.
John Hillman was born 4 December, 1819 in Westbury, Wiltshire, England ,and James Hillman born 17 November, 1822 also in Wiltshire.(2) Both are the sons of George Hillman and Susanna Browne.(3) Both are clearly brothers.
The Mays are more of a challenge. Isabella May was born in Scotland 3 October, 1822, and Mary May was born also in Scotland sometime in 1827.(4) Their father was Daniel May - proving it is becoming an interesting challenge. James Hillman married Mary May in Zone Township, Western District, on 21 December, 1847.(5) Unfortunately, these records from the Western District contain only the bride and groom’s names. Not those of their parents. The transcript of their marriage found on microfilm states that they were married by banns in Zone Township. Being married by banns suggests that the families were members of the same church - I know I am out on a limb here; but as far as I know there was only one Baptist Church in Zone Township at this time. In the 1880 United States Census Daniel May is found living with James and Mary in Sanilac County, Michigan. (7)The guess, and it is a guess, is that he is living with his daughter and son-in-law.
In the 1861 Canada Census John and Isabella (6) are living in Aldborough Township, Elgin County, Canada West. Daniel Hillman is found in the Village of Rodney not that far from the farm settled by the Hillmans. There seems to be a link. The evidence is at best circumstantial. We need documentation probably from the Scottish Archives. If it is available.
(1) The Ontario Archives has some microfilm available “Ontario Archives, The Marriage Registers of Upper Canada/Canada West - Western District, 1786-1856”; Ontario Archives “Western District fonds 1810-1931; As far as I can tell none of this is online. I am using 1851 as an arbitrary date. After this date it gets a little bit easier to find documentation.(2) Ancestry.com. “England & Wales Births and Baptisms“.
(3)marriage record for George Hillman and Susanna Browne, Ancestry.com, "England & Wales Marriages, 1538-1940".
(4) birth date for Isabella May found in her obituary, “The Rodney Mercury Sun” obituary October 4, 1906, and death certificate, Archives of Ontario, "Ontario, Canada, Deaths, 1869-1936 and Deaths Overseas". For Mary May I have to go with the date given in the 1880 United States Census.
(5) Ontario Archives, “The Marriage Registers of Upper Canada/Canada West - Western District, 1786-1856.”
(6) Their oldest son was named Daniel (it’s common in this area to name the oldest son after one of the grandfathers, or both if you are lucky - I am a case in point) ). His marriage certificate (8) puts his birth as 1840. It’s not necessarily accurate; however, it does suggest that John and Isabella were married some time before 1840- probably between 1837 and 1839. Also, Ancestry.com, “ 1861 Canada Census”.
(7) Ancestry.com, “1880 United States Federal Census.”
(8) Ontario Archives, “Ontario, Canada, Marriages, 1857-1924.”