1. What is name of sixth cousin?
From the information offered there most certainly is a link. Sadly, however, I do NOT have much data on the Estabrook family. What I have generally agrees with yours.
J.R. ESTABROOK (not I.R.?) b. circa 1816 or earlier married an ABIGAIL (nee unknown). They had in my record ONE daughter named Laura Jane Estabrook b. Jul 1839 d. 29 Oct 1909 m. Israel Pliney BLOOD b. Jul 1840 on 4 Jul 1866 at Portage, Columbia, WI. Israel was in civil war and thereafter disabled most of the rest of his life. They had children: Marcus D, Harvey G, Louisa A, George Monroe, Lilly Mabel Adelia, Leanna M, and Mary. I do believe that Laura Jane was married to MCDonald, another civil war apparant casualty ... where-upon Israel married the widow upon return from the war. Israel had brothers Calvin and Alvin also in the civil war. Both I believe stayed pretty much in the Columbia County area the rest of their lives.
Israel went to Dunn and later Barron County and lastly died in the Soldier's Home in Minnesota.
Israel's other siblings were: H. Dana, Mary, Loren, Lafayette, J. Monroe and Phoebe Loraine BLOOD (my Great Grandmother). She married Horace McKendry BARDEN. Parents of Israel are Ephraim B. BLOOD (adopted from name HUBBARD) AND Caroline LILLIE.
William ESTABROOK could very well be a brother to Laura Jane --no doubt. Any more siblings? Your I.R. 68 and Abigail 64 most likely are one and the same. No info on the rest of your names. Please keep in touch.