Carol, I've just been reading the top half of your message again (haven't tackled John Corkill yet).
1. I can't see where the Jane Christians fit in? (The "five potential deaths linking to these marriages".)
2. Where you say "Robert Corkill
We know that in 1779 he has a wife Jane. By the time he dies in 1807 he has a wife Catherine"
are you referring to the Robert b.1745 in Frances's deed, who was married to Jane?
I think the Robert who died in 1807 was his nephew, the son of John Corkill & Ann Kissag, but happy to be corrected.
Sue