Dear Deb,
I think the following are running certainties:-
1. Maria Richards Downman (wife of William Traies the artist) is the daughter of John Downman and Elizabeth Symons who married on the 4th April 1790 (IGI M50741)
2. Her father John Downman is NOT John Downman RA the artist for reasons you so clearly state.
I think the following are highly probable but not absolute certainties:-
3. Her father John Downman is the son of Hugh Downman and Ann (nee Richards) christened at Exminster in 1747 (IGI C050541)
and the brother of Hugh Downman the Exeter poet and physician christened at Alphington in 1740 (IGI C050171)
4. John Downman RA is a cousin of her father (ie the son of a brother - currently unidentified – of the Hugh Downman who married Ann Richards in 1738 at St Kerrian Exeter (IGI M050951)
The queries I have relate to the biography of John Downman RA:-
5. It states that in 1778 he married a second time to Elizabeth Jackson daughter of the William Jackson the Exeter composer and musician, friend of Gainsborough etc.
6. The only marriage of John Downman RA I have found so far is his marriage to Mary Jackson a daughter of William Jackson the composer at St Peter Cathedral Exeter in 1806 (IGI M052451). This marriage is not referenced in the biography but it definitely refers to John Downman RA as is confirmed in this British History online link – note 125.
http://www.british-history.ac.uk/report.aspx?compid=50576#fn125The biography does state that he was with his cousin Hugh Downman the physician at Exeter in 1806.
7. Did John Downman RA marry two of William Jackson’s daughters or have the marriages been confused? Is it possible that the 1778 marriage was to another Elizabeth (not nee Jackson)? In my limited experience of family history research, I have come across the husband of one sister then going on to marry another twice so it is not all that uncommon. It is possible but it is strange that this third marriage is ignored in what we can see of this apparently well researched biography.
The baptism of daughter Isabella Chloe that you have found supports the statement that John had a wife Elizabeth in 1786/7 and a daughter of that name so possibly my worry that the biography is wrong about other things such as her maiden name is unfounded.
I know too little about William Traies to speculate on how he and Maria came to meet and whether John Downman who was considerably older played a part.
Regards,
Bob