I do not have a wife for John Fernald. I think it was Miriam Lewis, but have no proof.
We know that a John Fernald was the father of Miriam Fernald born 1760-1770 (probably named for mother Miriam if indeed mother was Miriam Lewis). Book 17, page 55 of the York County Probate Records, shows that this John Fernald died intestate. His estate was divided between his two children, John Fernald 3rd and Miriam Lewis, wife of Paul Lewis. The division was dated 3 Dec 1794, but he, no doubt, died before that. Did the wife continue to live in the house and if so, why was she not named in the estate? I will have to dig out that copy of the estate division.
The Internet suggests that a John Fernald born ca 1698 (John 3, 2, Renald 1) first married Elizabeth Rogers in 1723/4 and had by her three children, one John in 1723. This John supposedly married in 1759 Miriam Lewis and had a son John III born in 1761, brother to Miriam.
But I have no proof as to parentage of John Fernald born 1723, and I have not seen any primary proof given elsewhere.
All these people pretty much were of Kittery and stayed there. There are so many John Fernalds, and looking at the Ancestry trees, one will post a spouse or line that is mistaken, and everyone just goes ahead and copies the mistake.