Jenny - some interesting points here that I have now studied a little further. However .......
That this Richard was the brother of Thomas can be nothing more than an assumption probably based on the fact that Peter James was a Quaker. Remember that the marriage of Ann to Thomas Pidwell and Elizabeth to Robert Luty both occurred in the Church of England so not all the family were Quakers. Richard did have a son named Peter so it is possible Richard was the brother of Thomas however there were two sons named beforehand. The first son's name is obscured by dark tape used to repair the page and the second son was named Thomas.
This is simply NOT POSSIBLE!
Elizabeth daughter of Richard James and Elizabeth Lade was born 21st December 1706 which means she would have been aged about 46 when she married Robert Gendall!
And the last child of Robert Gendall was baptized in March 1777 at which time Elizabeth would have been 70!!!
Whether or not the wife of Robert Gendall was related to Thomas James is difficult to say but I believe I can tell you who this Elizabeth James was. The starting point for her identification begins with the following two points:-
1. Robert Gendall was baptized 26th November 1731
2. There were 13 children between 1754 and 1777
As I have mentioned in many other posts the formula I work on is that age 48 is about the maximum age for a woman to have been having children. I can think of just one occasion where that might have been exceeded and even then I recall that the mother would have been 49. So - with the last child baptized in March 1777 if Elizabeth James had been as old as 48 it means she could have been born no earlier than late 1728.
Similarly I begin with age 16 as generally the earliest age for women to be having children. As the marriage was in 1753 then the latest likely birth for Elizabeth would have been 1737 so the year range we need to look for a birth/baptism of Elizabeth James would be between 1728 and 1737.
Based on this formula there are just two possibilities at Madron//Penzance:-
1. Elizabeth daughter of Thomas James bp. 15th April 1729 at Penzance
2. Elizabeth daughter of Richard James bp. 17th December 1733 at Penzance
If daughter of Thomas then the most likely marriage 'seems to be' that of Thomas James and Ann Gendall in 1719. A Thomas James married Sarah Pender at Madron in 1729 but that was in August which was four months AFTER Elizabeth was baptized!
If Elizabeth was the daughter of Richard James then the probable marriage is that of Richard James and Constance Osborne (both of Penzance) which took place at Madron 6th January 1731.
The next step in trying to identify Elizabeth was to check for possible burials and I found the following which are the most likely:-
Robert Gendall buried 29th November 1803 at Madron
Elizabeth Gendall of Penzance, widow, age 84 buried 29th July 1817 at Penzance
This Elizabeth, if her age is accurate, would have been born about 1733 which then suggests the wife of Robert Gendall was the daughter of Richard and Constance James.
Returning to an earlier post and you made this comment:-
Aside from indicating brother Richard had 'heirs' there is nothing in the Will of Thomas James that I can see that specifically says Richard had a granddaughter named Elizabeth. The children I have found in the Quaker records for Richard and Elizabeth are:-
Elizabeth born 1706
illegible son born
? - name might be Richard but it is almost totally obscured as is the year of birth which might be 1709 or 1710.
Thomas born 1712
Peter born 1715
David born 1718
If the first son was named Richard then he could have been the one who married Constance Osborne but it would also suggest that he renounced the Quakers.
One final thing to add for now is in reference to the dates, particularly as used by the Quakers. Remember that the period we have been dealing with is mostly before 1752 so the Julian (Old Style) Calendar was in use. What you also need to know is how to interpret the way dates were recorded in the Quaker records!
Go to the following link for a very good explanation (with diagram) of the Quaker Calendar:-
www.swarthmore.edu/friends-historical-library/quaker-calendarAs you will have seen in some of the records you have looked at the dates are recorded a little differently to those in the Parish Registers. e.g. 'borne the 4th day of the 2nd month' or 'borne the 8th day of the 11th month'.
Using some examples you have quoted:-
These are both recorded as 'of the 2nd month' in the Quaker records and you have, as most people would, interpreted that to mean that the marriages took place in February. However, that was NOT the case!
Prior to 1752 the year began on 25th March and ended on 24th March so to all intents and purposes the first month of the year was March. So when the Quakers record that a marriage took place in the '2nd month' it actualy took place in APRIL.
I am sure that will take some getting used to but if you save a copy of the diagram and keep it handy I am sure you can work it out.
CT