Hello, Steve ~
I did a bit more research on the Tennessee Cole's. This may or may not be a coincidence. But I found a U.T. Cole (abt. same age) in that same 1850 census record (2 pages over) for Mary E. and Elizabeth Stobaugh.
If they are in fact the couple in your profile, I had a couple thoughts. One being, the brother-in-law reference could have been a casual one. Instead of saying, his wife's brother-in-law. Or Elizabeth could have been illegitimate etc. Either one would be difficult to confirm at this point.
Here is U.T Cole in 1850 (with possible brother):
"United States Census, 1850," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MCDZ-Y3F : 9 November 2014), U T Cole, Decatur county, Decatur, Tennessee, United States; citing family 21, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).