Sorry this isn't more helpful, but I'm just writing to tell you that I don't think there are any newspapers online at the moment for that date range in Ingham County.
Actually, there is the Jackson Citizen Patriot on genealogybank that covers those years (even though it was in Jackson, they have tons of news from Ingham in that paper), but I did a search for your relatives and didn't find anything.
I also checked this book and found neither: "Marriages and deaths mentioned in the Lansing State Republican, 1855-1870" so don't bother with that book (or the newspaper it covers).
It looks like you might have to order some microfilm from LDS. You should get these two:
1. Probate records, 1840-1904; probate indexes, 1835-1933
author: Michigan. Probate Court (Ingham County)
2. Abstracts of the early probate records of Ingham County, Michigan, 1838-1869
If you find the probate file number, the archives should be able to get it for you right away. Or, you can e-mail them at firstname.lastname@example.org
and they can probably look it up and retrieve it for you (but that might cost more). There is more information on their website, but I got a post removed on this message board for posting a link once so I don't want to do that again. Just search for the Archives of Michigan and you should find it.