them 10.5.1800 surely referred to James Marshall & Sarah Elwes
below are notes from my correspondence with Mark Philp whose article Sarah Elwes' calling was published in Bodleian Library Record April 2011
John Elwes divorced Sarah Elwes in Ecclesiastical court in 1796, she appealed; the Court of Arches hearing found in John Elwes favour; she appealed to the High Court of Delegates. But when he died (about 19.4.1817) it was mentioned that he had two sons (Derby Mercury May 1, 1817).
On 14 January 1818, his wife, Mrs Elwes was reported as dying, aged 52 (in Bury and Norwich Post)
Sarah Elwes died on 26 Dec 1817 and there was a sale of her effects reported in The Times for 12 January 1818 (i.e., before the reported death of Mrs Elwes of Portland Square).
To complicate matters there are claims that John Elwes gave evidence in a trial some time after his death (Jackson’s Oxford Journal 12.1.1818).
John Elwes will PCC 1817, no mention of Sarah. His son John Meggott Elwes was about 10 when the will was written, he also mentioned his son Henry, and his brother George (who must be the one involved in the 1818 forgery case) and the Rev Charles Mosman.
Capt Haynes RN was Thomas Haynes (list of Naval Officers in Bod LRR B3.251) and died at Exeter early Jan 1789 or late Dec 1788 (newspapers), but Sarah's marriage to him doesn't seem to have been in the papers and there were too many Thomas Haynes (or Haines) marriages to Sarahs on Ancestry and Family Search to be sure which one, the most likely was to Sarah Allen at Allingham Dorset in 1785. She would have been due a pension but I couldn't find their marriage certificate in the Naval officer's records at Kew. The will of Josiah Oake PCC 1840 referred to her as "my late worthy cousin german Sarah Elwes", so her maiden name could have been Oake but a cousin by blood may be through one or two surname-changing marriages
John Elwes (Sarah's husband) seems to have fathered a son Henry in 1788 by Margaret Olley Elwes at Stoke, Suffolk, maybe they were married or not, unlike most marriage registers it doesn't say whether he was a widower when he married Sarah Haynes at St Anne Soho. Henry married Susan Hamond in 1813 and the first bit of John Elwes' will concerned their marriage settlement. The other son, John Meggott Elwes, was born about 1805, at St Marylebone according to 1851 census but probably not baptised there or it should have shown up on Ancestry etc