Kathleen, The LDS 1880 fed. census shows Eavard J. WEATHERWAX (61y) a blacksmith in Pittstown with wife Maria M. (61y) and ma-in-law Mary MILLER (92y). Thus the George J. WEATHERWAX listed adjacent to Jacob F. WEATHERWAX in the 1860 fed. census must surely be Edwin J. WEATHERWAX, the sibling of Susan Eliza WEATHERWAX Hibbard Inman. So although the John Inman diaries seem to imply that Jacob F. WEATHERWAX might be a brother on his visits to the Inmans, I surmise that (although just a distant cousin to the siblings Susan, George, Edwin, Kate, Jene) he must have been quite close to them growing up--and particularly close to Edwin, since they were neighbors in 1860 and both were blacksmiths by trade (perhaps they even worked or apprenticed together as smiths).
Such a situation is not new to me. Several of my mother's first cousins (all descendants of Martha Sophia W'WAX and Henry Ozeander KERNS as am I) came from their home in Alberta to work on my grandfather's farm and lived with the family in Garfield, Whitman Co, WA (the same area where Martha and H.O. settled after leaving Iowa). My mother was especially close to one of them, Ralph KERNS, a paratrooper killed in action in WW II. My mother named me after him (three of my second cousins are also named after him). It also seems that the W'WAX's (at least my line) are very much family oriented--in particular family reunion crazy! I recall seeing at some site on the Web that all but two of the children of Thomas and Jane W'WAX had a reunion in Iowa in early 1900's (to include Martha Sophia). I know that the descendants of Marthaand H.O. KERNS have had numerous reunions since then, and since about 1978 there have been biennial KERNS reunions (even years, of which I have attended about eight) alternating between various locales in Washington State and BC/Alberta Canada where the majority of these descendants live.
After reading the John Inman diaries, if indeed Thomas is a sibling, why wasn't he ever mentioned, since he lived close by?? Thomas in Kane Co, IL was also close by Susan Eliza W'WAX Inman and Kate W'WAX Slade in Boone Co, IL in the early 1850's. Could there have been some family squabble that resulted in Thomas being treated as a pariah by the rest of the family? Anyway, this is just some speculation on my part.
P.S. I have enjoyed the photos you have made available on the Web. I particularly like the one of GGGgrandpa Thomas as one of the "Greybeard Regiment" in the Civil War.