Here’s what I think:
12 Apr 1852 JM Martin Sr. (1834-1901) married Polly Ann Cochran (1833-1876)
4 Jun 1859 JM Martin Jr. (1859-1900) was born to PA Cochran
12 Apr 1877 JM Martin Jr. (1859-1900) married SJ Ross (born abt 1856-57)
21 Aug 1878 IS Martin was born about 16 months later to SJ Ross
1880-1882 SJ Ross died sometime
15 Apr 1883 JM Martin Jr. married Mary Elizabeth Cochran
The relationship between Polly Ann Cochran (1833-1876) and Mary Elizabeth Cochran (1861-1937) is unknown.
My guess is that Polly A and Mary E were cousins of some degree, but of different generations.