Janis, a great deal of research on the English Churchills has been done by Bill Churchill, who posts frequently on this forum but has recently been occupied by more pressing matters.I am afraid your posting is inaccurate, and I thought it important to correct it before it takes on a life of its own.This response is drawn directly from Bill Churchill's work.
The William to whom you refer was one of two sons of Thomas of Rockbeare, who was born between 1465 and 1470 in Rockbeare, Devon.His elder son was Thomas of Rockbeare, born between 1490 and 1495 and died between 17 May 1577 and 24 December 1577 in Rockbeare.The Rockbeare, Devon, Churchills who descend from him include the immigrant to America, John of Plymouth.
The younger son, William of Dorset, whose wife as you say was Mary Creuse, was born between 1490 and 1495 and died before 11 July 1583 in Piddlehinton, Dorset.As you say, he had sons John, William, and Roger, though he also had a fourth son, Alexander.The Marlborough line is, as you say, descended from Roger.
John Churchill, the eldest son of William, was born about 1512.Note that your birth date of 1561 would have him born when his mother, Mary Creuse, was about 71, as she was born about 1490.John married Edith Bond.He died between 15 April 1557 and 25 August 1557.He had three children, William, Elizabeth, and John.Younger son John had two daughters, Anne and Elizabeth.William, born in 1541, married Missy Swayne and had six children, the first two of whom were sons, William and John.
These two children of William of 1541 and Missy Swayne are great-grandchildren of William of Dorset and the only two male Churchill-surnamed grandchildren of John of 1512.They cannot be siblings to Josiah of Connecticut, who was probably born in the 16 teens.The elder, William, was born about 1565, and the younger, John, was born about 1566.
Elder son William had three children, Joseph, John, and Thomas, all born before 1600.Younger son John had fourteen children born between about 1596 and 1615.None of them were named Josiah.
It apears that this John may be the John that you believed to be the grandfather of Josiah, as his death date of 1521 is the same as what you have for Josiah's grandfather, hs birth date of about 1566 is close to your 1561, and his wife's name of Eleanor Miller is close to your Eleanor Meller.However, John's chidren are too young to be the parents of Josiah of Wethersfield.
Clearly, then, Josiah of Wethersfield cannot belong to the Dorset line of descent beginning with William of Dorset and then John.
The line of descent for John of Plymouth, Massachsetts, is Thomas of Rockbeare (Thomas being the brother of the William of Dorset you thought was forebear of Josiah's line), George of Rockbeare, Thomas of Wolsen, and John of Plymouth, Massachusetts.John was one of six children, the youngest of whom was born in 1613.
In addition to the absence of any historical records that would identify where, when, and to whom Josiah of Wethersfield was born, genetic testing demonstrates conclusively that he could not have been a brother of John of Plymouth.The haplotypes of John's and Josiah's lines differ in two genetic markers. Y-DNA markers are inherited from fathers, with mutations rare.Brothers differing in two markers is statistically almost impossible. While conceivably Josiah might have descended in the Devon line from another son of Thomas of Rockbeare (oldest son William being a possibility), it is equally possible that he was from another Dorset line or from an even earlier branch off the Churchill family tree.
The search goes on.