Durhams 18 19 Century

Its a while since I posted anything and since then I have established the Durham family descended from Cornelius (4; my number)
Durham and Ann Morris and wondered if anyone could assist me in proving or filling the gaps?

Cornelius (4) was born ca1775 and died in London in May 1817. He appears in the 1802 Westminster Poll Book where his address is give as Craven Buildings, St. Clement Danes and his occupation as a Clerk. He married Ann Morris in St. Brides Church, Fleet St. on 15 July 1800. She was born ca1771 and died on 18 June 1843. Family anecdotes refer to her as Ann Morris of Hereford but give no further information.
She was granted administration of her husbands estate on 1 September 1817 as he died intestate, possibly in Littleham, near Exmouth, Devon (The parish Register gives his age as 43, which fits)

They had 5 children, Sophia Ann born in 1801, Henry (these two do not appear in family anecdotes but records show that they existed), Edmund, Cornelius Beavis who married Mary Cuisset and John Farr.

A possible sibling of Cornelius is William who was born ca1772 and Married Jane Pagett on 5 August 1792 in St. Mary's Church, Enville, Staffordshire. They had 7 children the youngest of whom was Sophia who was born in 1806.

Family anecdotes refer to a Sophia Durham who married a Mr. Beck with no further information. A Sophia Durham married William Beck (a jeweller) at Old Church, St. Pancras on 14 January 1824. William Beck died in June 1840 and a Sophia Beck died in London on 13 February 1849 but another Sophia Beck (probably the daughter of William and Sophia) is known to have immigrated to Australia/New Zealand between 1841-1850. Sophia Beck and three children John, Mary Anne and George is shown as staying with Ann Durham in the 1841 census. Sophia is shown as being of independent means. Ann had become a Lodging House Keeper after the death of her husband. I have been unsuccessful in finding a 10-15 year old Sophia Beck in the 1841 census, but the New Zealand descendants claim descent from William and Sophia.

Martha Durham born ca1781 is another possible sibling. She married a Henry Palmer but I can find no record of a Durham/Palmer wedding, but Martha may have married twice. Certainly Martha and Henry have 5 children among whom are Martha (2) Palmer and Elizabeth. Cornelius Beavis is described as a cousin when staying with Martha Phillips nee Palmer in the 1871 census, Elizabeth Biddlecomb nee Palmer described as a sister is also staying with her. Both these women accompanied Cornelius Beavis and his wife Mary on a tour of the continent in September 1853. This is shown on the Passport Cornelius obtained

Little or nothing is known of Cornelius (3) who was born ca1751 but family anecdotes refer to a Durham of Devils Bridge. I have found four places of that name. Aberystwyth which had a large mining and quarrying centre in the 1700's appears the most likely as Cornelius could have worked there.

Cornelius (2) was born in 1711 and christened in St. Andrews Church Holborn on 16 December 1711 and died in 1872.
A Cornelius Durham was elected as an Overseer in the Isleworth Parish Middlesex and as an Overseer with William Reinell on land and houses on 14 June 1770. He was also to the will of James Clerk as shwon in the Parish Account book of Ockley. He may have been married twice once to an unknown and the second Jane Toone. There are four Fleet Registers showing this marriage on 21 21 June 1971 all have sightly different detail but the same date. A Jane Durham is shown as buried at St. Mary's Whitechapel on 4 June 1783 and a Cornelius Durham buried at St. Mary,s Church Chatham on 4 June 1782

A Cornelius (1)/ Christo Durham is shown as marrying a Rachel Roberts on 1 January 1700
She was born in Wales on 2 March 1675 and died in June 1745

I'd be grateful for any assistance