This likely won't be of much help to you but who knows.
There are two Duncan McGregors in Horton, one born 1827 who married Margaret McInnes and yours born 1833 who eventually married Marion Hart.
Parents are different.
With the Scottish naming system there will be other Duncans in borh families.
On 1891 census there is Marion Hart with her McGregor sons, as a lodger with Duncan, aged 52, and what looks like some of his siblings.
On their marriage rego it says Duncan is a bachelor.
Duncan of above family, b 1869, died 1938.
There is also a Duncan, aged 8, died 1881 of diphtheria with informant Duncan McGregor of Horton.
Also a Mary McGregor, 11, died 1881 of diphtheris with same informant information.
Think they are from Duncan/Margaret.
A Duncan McGregor was born 18 June 1873 at Horton to a Duncan McGregor and Margaret McInnis.
1901 has a Jannet McGregor b 04 May 1890, immigrated 1895 with Duncan and sons as a domestic.
Jessie's headstone says Jessie McGregor 1888-1946, native of Scotland.
20 July 1870
Duncan Hart, illegitimate, Mother: Marion Barr Hart
Willam Hart, illegitimate, mothe: Marion Barr Hart
Same fellow or twins?
Can you get some obituaries? The old ones had lots of information on them.