Morning Neil-

I'm afraid I can't help you with Mary's parents, but perhaps they are listed on her death certificate.
She was b. 15 May 1848 and d. on 20 January 1935 in Pontiac, Livingston, IL at age 87. Her death certificate # 0002127.

As for Charles...found a couple of sources indicating that he was b. 14 Oct 1847 in Grand Rapids, Kent, MI & d. 24 Oct 1911 (probably in Pontiac, Livingston, Illinois).
Charles was the son of Levi H. Bigelow b. 1816 Reading, Steuben, NY and d. 14 March 1885 (again, probably Pontiac, Illinois) & Lucy F. (Fisher) Bigelow d. 17 Jan 1868.

Hope this helps a bit in your search.
Paul