As far as I know, all the Soverhills are descended from Abraham. He seems to have been the only immigrant with that last name.
According to my notes, Isaac and Samuel Soverhill both came from Newark, NJ and were among the founders of Arcadia, NY in 1798. (I've also found some indication that they were in Bradford County, PA for a time, though since Isaac had married Elizabeth Dobbins in New Jersey on 6 Jan 1796, they can't have been there very long.)
A website I found a couple of years ago said that Samuel (born 6 Sep 1769) was the son of Samuel Soverhill, Sr. (b. 1733) -- and that elder Samuel has to be the son of Abraham Soverhill and Jemima Adams, who was born 1 Mar 1733/34 in Simsbury, CT.
My best guess is that Isaac was probably the younger brother of Samuel Jr., but he might also have been a cousin. There were a lot of Soverhills in New Jersey by the late 1700's, and I've never gotten a clear picture of how they were all related.