The information I have assembled on Robert Hortop & Susannah Sweet's children is as follows:
1.John, b. 1746, North Lew, Cornwall, England; d. 10 Nov 1826, Lamerton, Devon, England.He married Anne Johns on 24 Apr 1778 in Morwenstow, Cornwall
2.William, b. 9 May 1750, Beaworthy, Devon, England; d. Jun 1823, Tresmere, Cornwall, England.He married Mary Crosman on 23 Feb 1778 in North Lew, Cornwall.
3.James, b. 1753, Beaworthy, Devon, England. Emigrated to Australia on the Ship Charlotte in 1788.
4.Richard, b. 1755, North Lew, Cornwall, England
5.Roger, b. 1759, Bratton Clovely, Devon, England; d. 26 Nov 1811, North Lew, Cornwall, England.He married Joanna Hall on 2 Apr 1783 in Lifton, England.
6.Phillip, b. 1762, North Lew, Cornwall, England; d. 10 NOv 1826, Lamerton, Devon, England
7.Jane, b. 1767
As you can see, this is sketchy at best and I don't have evidence to support all of it - I continue to search!
I haven't found a Susannah Hortop as one of Robert's children. I did find a Susannah who married a Robert Hortop:Susannah......., b. abt. 1793 in Broadwoodwidger.She married Robert Hortop, son of John Hortop and Anne Johns.They had a daughter Susannah Porthanous Hortop, b. 1823 in Lamerton, Devon.Perhaps Porthanous was her mother's maiden name?
Do any of these fit with your Susannah?
The other "Susannahs" I have found are
1.Susanna Hortop, b. 8 May 1824, Lanreath, Cornwall; d. Jul 1866; married a William.... She was the daughter of Anthony Hall Hortop, b. 11 Jul 1790 in Germansweek, Devon.
2.Susannah Hortop, b. abt 1779 in Morwenstow, Cornwall; she was the daughter of John Hortop and Anne Johns.
3.Susannah Hortop, b. 1802 in Broadwoodwidger, Devon; she was the daughter of Roger Hortop and Joanna Hall
I think your theory is a sound one but, as you say, the evidence is circumstantial at best.
Thanks for sharing,