Here is a little more information on the family. James and Annie Sophia (MacFadyen) MacKinnon (with the name spelled as 'Mac') are buried in the Newtown Road Cemetery in Port Hastings. Nancy MacDonald has done a transcription of, I believe, all existing grave markers there and her work is available at:http://www.capebretongenweb.com/Cemeteries/cem138.html
So James M[a]cKinnon died in 1929 and Annie in 1947. As well, they apparently had an additional child, Walter James, who died in infancy (10 months). Also buried with James and Annie are two of their sons, Ian Hector , who died in 1988 and Roy Laidlaw, who died in 1987. Knowing that Laidlaw McKinnon was really Roy Laidlaw I could find his birth record and he was born Sept. 28, 1914. I assume neither Ian Hector nor Roy Laidlaw ever married but I could be mistaken.
I also discovered one marriage for the children of James and Annie and that was for James Calvin, who went by Calvin (1908-1962). His grave marker is searchable and a photo available and on the grave marker, so buried beside him, is the name of his wife, Roberta E., who died in 1995 (b. in 1921). Her obituary is publicly available and gives her full maiden name (Roberta Elizabeth Reynolds) plus the names of their 3 children, who were, at least in 1995, still living and in I think Inverness Co. and not too far from Port Hastings.
Considering that the youngest of James and Annie's children, Howard Kimball, would today be over 101 I think it is safe to say that any of James and Annie's children that your grandmother knew would now be gone. There are going to be some of the grandchildren of James and Annie still living and they would presumably be in their 70's and probably into their 80's.
Surprisingly it seems that here at Ancestry.ca there is no data related to this James and Annie Sophia McKinnon and family, and no user trees that include them.