Joni ~
In William and Sarah Robinson's 1870 census there was a George Robinson living nearby. I searched records to see if he was Williams younger brother. I did find a possible family for William Robinson that could be traced through Pennsylvania, New York and then to Michigan. The names and ages were pretty consistent with the exception of William. The earlier records list the entire family's birth place in the States (Penn. and N.Y.). Which is inconsistent with William's later census records. Birth places are often wrong in some records. If that is the case here it would seem to be intentional.
I'll post a couple records here of George and William Robinson with parents. You can find more at FamilySearch.com. You would know better than me if it is the correct family.
Let me know if you need help finding the other records.
1850 census: "United States Census, 1850," database with images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/M4HY-BVN : 9 November 2014), Ralph E Robinson, Benton, Luzerne, Pennsylvania, United States; citing family 32, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).
Death record of possible father:
"Michigan Deaths, 1867-1897," database with images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/N3NC-KXM : 12 December 2014), Ralph E. Robinson, Sep 1877; citing p 10 rn 36, Evart, Osceola, Michigan, Department of Vital Records, Lansing; FHL microfilm 2,363,665.
Marriage record of George Robinson (2nd marriage) w/parents:
"Michigan, County Marriages, 1820-1940", database with images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/FCNK-7ZV : 25 April 2016), Ralph Robinson in entry for George Robinson and Mary Mcdonald Brown, 1903.
Ralph 1870:
"United States Census, 1870," database with images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/MHHK-XPQ : 17 October 2014), Ralph Robinson, Michigan, United States; citing p. 28, family 229, NARA microfilm publication M593 (Washington D.C.: National Archives and Records Administration, n.d.); FHL microfilm 552,170.
Good luck!