This is the information I have about James and Nancy McEwen.
this Newfield Village Cemetery has listed the following McEwens
McEwen, Alexander R., son of James & Mary d. Nov 19, 1831 10y 9m 10d McEwen, Ada A. dau of James & Nancy d May 15, 1861 6y 3m 16d McEwen, Ellen dau of James & Nancy d April 10, 1859 27y 11m 20d McEwen, James d. September 11, 1867 83y 4m 3d McEwen, Martha A. wife of A M Baker d Sept 16, 1885 73y McEwen, Nancy wife of James d June 6, 1870, 80y
1850 Census - Newfield, Tompkins County, NY, Roll 606, Book 1, Page 312
the ages of are close they both should be about 70.I also don't believe Nancy was born in Ireland.
1870 Census - Ithaca, Tompkins County, NY, Roll 1104, Book 1, Page 263
Baker, Merritt A57Boat Builderborn NY Baker, Martha A50born NY (cemetery above) Smith, Eliza35born NY McEwen, Nancy79born NY
This looks like the family from the Cemetery Listing above however there is a problem with Nancy's death date.Unlike the 1860 Census, the 1870 Census has her correct age.This Census was taken July 16, 1870 and according to Nancy's Cemetery listing above, she died June 6, 1870.
Martha age 47 shows up with Merit age 47 Boatbuilder on the 1860 Census - Ithaca, Tompkins County, Roll 868, Book 1, Page 461.
I haven't found much else on the other two McEwen kids.