It looks certain that John Fernald and Miriam Lewis are the parents of your Miriam who married Paul Lewis.
Jonni Sue's web site also has Miriam Lewis married to Major William Haley in Kittery but the date is off 100 years! It should be Nov 1773.
So then, the surviving children of John Fernald and Miriam Lewis are:
John Fernald (born abt 1761) Miriam Fernald (b. 1765-1770) James Fernald (a minor in 1782 probably born bef. 1770) Benjamin Fernald (the youngest born bef. 1773)
Jonni Sue has that their mother, Miriam Fernald died in 1794. Since John, the son of John and Miriam was born abt 1761, and Miriam was born 1765-1770, They must be brother and sister. I have not seen any records for his passing yet. John married Martha Jones and they had at least 2 children, John and Dolly.
I believe the line descends as follows:
1. Miriam Fernald and Paul Lewis 2. John Fernald and Miriam Lewis 3. John B. Fernald and Dorothy Main 4. John Fernald and Sarah Hinks 5. John Fernald and Mary Norman Spinney 6. Renald Fernald and Joanna Warburton