Margaret, I would have accepted that the 28 yr age difference, between Humphry & John as stated in your ebook was a typing error, but for the fact that it was followed by "when John was four, Robert died. By this time Humphry was making a name for himself among Scientists and Socialites alike.
When in fact in 1794 when his father Robert died Humphry was 16 & at Truro Grammer School & it was a year after this, that he was apprenticed to, John Bingham Borlase, a Penzance chemist. While it was during this period that his interest in Chemistry began.
My research differs so greatly from your claims, although their are common factors. I agree it is very probable that their are living descendants from the marriage of Grace & George Rolleston, but not from Sir Humphry Davy Rolleston as you state. As both his sons seem to have died childless. Son Archibald Davy & wife Helen, also had a daughter Helen, but again she seems to have been unmarried & childless.
I believe their is evidence to support the following; John & Margaret married in Tadcaster in 1830 & straight away travelled to Malta where John returned to his post & where Elizabeth Mary, Grace & Archibald where born.
The Davy's did not return to England until 1835, when John Davy took took up a post in Kent, where Humphry & John Davy were born. In c.1840 John took up a post in Turkey for a year & Margaret joined her mother & sister in Grassmere & later Edinburgh where I believe John joined her & the family. After the two little ones died in Edinburgh in 1844, I believe the Davy's decided to move permanently to the Lake District & had Lesketh How built, while Margaret & the children moved in, John was again appointed over seas to the West Indies he returned in 1848 & Elizabeth Mary died in 1853. I know nothing of the false grave you mention.
You previously said; "Archibald was definately illegit. The other 3 boys were paid for to go to school in Edinburgh by Margaret,s grandfather. John had to pay for A. himself to go to school at Rugby. Luckily Thomas Arnold also lived in Ambleside!"
All the evidence I have found points to Margaret & John having three sons & one surviving son (Archibald). While both of Margaret's grandfather's were dead. Her Paternal grandfather died in the c.1750's & her maternal grandfather in the same year as she was born 1798. While Margaret's mother Eliza Fletcher, was a great friend & admirer of Dr Arnold & insisted another nephew had the best schooling available when his father died, Rugby!
I am baffled with some of your Davy tree. The father of Philippa Davy b.1855 & married to W.H. Toze seems to have come from Devon & doesn't seem to have a connection. While Margaret's sister Mary did have had a son called Edward John, I don't believe Margaret & John did & I while I know of Humphry & John's cousin Edmund (son of William Davy), I couldn't find Edmund Davy Penzance surgeon c.1830.
Incidently, I did'nt think that I was connected to Elizabeth Mary Davy. On the other hand my Grandmother's, mother's family, came from Madron & Humphry's uncle William settled in Madron & is said to have a large family (possibly 10 children),which is where my original interest in the Davy family, originated from.