While this is not my line. I have been working with Virginia B. who is amassing data on this line. The research is not yet definative, so keep in mind that this is a work in progress, but the clues seem to be heading towards the right track.
I think the Samuel you mention is a cousin. Samuel b. 17 Aug 1756 was the son of Humphrey Fernald and Dorothy Fernald. Samuel married Deborah Griffith.
The Portsmouth NH North Church records indicate Margaret may have been the child of William, son of John.
Ezekiel Fitzgerald b. 16 Oct 1780 d. 23 Feb 1829 m. 08 Nov 1804 Margaret Fernald b. 30 April 1783 Portsmouth, NH bp. 1786 and died 9 Aug 1866. Dracut, MA. of consumption. (death record has 83y 4m 9d, marker has age of 82) They are buried at Old North cemetery in Portsmouth, NH
The children of Ezekiel Fitzgerald and Margaret Fernald are:
Reuben Fitzgerald Ezekiel Fitzgerald George Fitzgerald Elizabeth Fitzgerald Harriet Fitzgerald Maria Fitzgerald
These are the clues from the North Church records of William Fernald and wife: baptisms
1779, 26 Sept,John and Katy of Wm Fernald & wife 1784, 26 Sept, Wm. and George Sons of Wm Fernald and wife 1786, 23 Jul,Margaret dau of William Fernald & wife 1788, 24 Aug, Mary Griffis dau of William Fernald & wife
1757, 24 Jul, Wm. Child of John Furnell (suspect this is the same William, father of Margaret)
1715, 24 Jul, John is baptized. (suspect this is John, father of William and believe he is a son of Amos)
Also on 27 May 1715, Amos and Humphrey, sons of Amos were baptized.
It seems likely that William and wife may have named 2 of their children after his parents.
We suspect that they are John Fernald and Katherine Staples.
If so, the line from Margaret to Renald is:
Margaret Fernald and Ezekiel Fitzgerald William Fernald and wife John Fernald and Katherine Staples Amos Fernald and Mary Woodman John Fernald and Mary Norman Spinney Renald Fernald and Joanna Warburton
We looked into William's daughter Mary Griffis (perhaps Griffin or possibly Griffith.) There was a Mary G. Fernald who married Reuben Welch 30 Sep 1806 then we found a Mary G. Welch who married Samuel Gerrish on 6 Apr 1809. Some records call her Polly Fernald and some Mary Fernald. So we believe they are the same woman. Samuel Gerrish is connected thru deeds and estates to this family and Ezekiel Fitzgerald Jr. had Samuel Gerrish as his guardian after Ezekiel Sr died in 1829. The connection appears promising. The kicker or what may be another clue, is that Mary G.'s death record lists her parents as James Fernald and Phebe. I can find no internet data base sources to reveal who James and Phebe are yet, neither have we found out who William's wife is. It would take, for perhaps, William to have been named William James Fernald, if all of this is to fit!!! I suspect the name Mary Griffis is some how connected, (Perhaps Phebe was a Griffin! Or perhaps William or one of their relatives was married to a Mary Griffin) There were a few Grifffin's and Griffiths in Portsmouth at that time.
If we find anything significant, I'll continue this post to let you know!