I may not have ironclad proof of a relationship, but then I certainly see nothing to prove that these families are UNrelated.
Do two men have to have sons named William born in THE SAME YEAR in order to be brothers?Certainly not.More likely, both Cornelius and Anthony honored their father William by naming sons for him.In the case of Cornelius, there seems little doubt that he named his oldest son William for his father.
If you believe that Anthony Seale / Sale Sr. is the son of the William Sale / Seale who came in 1655 (really 1656, as the land grant to John Wood based on transportation of Wm. Seale and 19 others would have been dated Jan 1657 on the Gregorian calendar), then you should believe that Cornelius and Anthony were brothers, because it was Cornelius who evidently fell heir to the real estate of William Sale the immigrant under primogeniture.
Compare the 1704 rent roll for Essex County, where "Widow Sales" is shown as the owner of 1150 acres, with the later lists where that land is in Cornelius' name.I doubt that it was done by deed (as opposed to inheritance) as there is no deed of record to effect such a transfer.There was no one named Sale / Seale / Sail / Sales buying land there before 1704 other than William, except for the 73 acres Cornelius held in his own right as of 1704.That seems to argue strongly for Cornelius as the son of William.
The Sale and Seale spellings are used interchangeably on the earliest records in tidewater -- as well as Sales, Sail, Seal and even Salle (though there's a Huguenot family with the latter name further south that's likely not related to us), so it would be unwise to base everything on the presence or absence of that first "e."
In the 18th cent., your Anthony seems to have favored the extra e, as did William Jr. (see, e.g., 1710 lawsuit against the executors of Sam Cox), while Cornelius and his descendants did not.That doesn't prove that they weren't one family at the beginning.
That all three of these men -- the contemporaries Cornelius, William [Jr.] and Anthony, had sons named Anthony is strongly suggestive of a close relationship; very probably brothers in my estimation, unless the tidewater records of William Seale / Sale / Sail etc. from the late 17th cent. actually refer to more than one person.