Well, Richard Harrison definitely would NOT be the son of George Fulton Sr if he is the son-in-law. This would definitely lead one to believe that is the wife's maiden name. The the grandchildren of George Fulton line up well with the children of this Richard Harrison and wife Ellen S Unknown, I'd say it is now known.
One thing I did notice is PLEASE put citations preferably with links for sources.
United States Census, 1910 is not an acceptable source.
"United States Census, 1910," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:MPKT-2BB : accessed 18 December 2018), Richard E Harrison in household of George Fulton Sr., Kossuth, Manitowoc, Wisconsin, United States; citing enumeration district (ED) ED 21, sheet 13A, family 137, NARA microfilm publication T624 (Washington D.C.: National Archives and Records Administration, 1982), roll 1719; FHL microfilm 1,375,732.
NOW THAT is a source.
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https://www.wikitree.com/wiki/Space:Sourcing_Primer_-_Instructional