Ok so going with the fact that often in my family I have found brothers marrying sisters, this is what I am looking at now....
These are my workings:
Brook
William Brook (probably bap. 24 October 1786 in Biddenden) married Mary Mitchel (bap. High Halden, 27 December 1794) in Hellingly, Sussex, 7 July 1817 (see my post 47).
Their son William Brook (bap 16 August 1818 in Biddenden) married Sarah Larking 7 August 1842 in Lewisham and then married again, this time in Biddenden, on 4 June 1867. His second wife was Sarah Carter.
In 1871 William Brook (bap 1818) and his wife Sarah lived in Pope Street, Eltham, with their son Charles and their daughter Eliza but at the time of the 1871 census they were staying at Brickwall House in Biddenden.
Brickwall House, Biddenden in 1871
John Mitchell and Sarah Mitchell were the brother and sister of Mary Mitchell who was the 1871 William’s mother.
Mary, John and Sarah were the eldest children of what became the Hellingly Mitchells. They were all baptised in High Halden; Mary - 27 December 1794; John - 13 August 1796; Sarah - 13 May 1899.
Note that there appears to have been an older brother William Mitchell, born High Halden c1793 (no baptism found) who married Sarah Parris in Hellingly on 27 December 1814 and became the father of the Hellingly/Rye lot – see e.g. 1861 census RG9 Piece 557 Fol.115 Page 29; 1851 Census HO107 Piece 1634 Fol. 373 Page 23; 1841 HO107 Piece 1109 Book 5 Fol.50 Page 17.
Their children baptised in Hellingly appear to be: Henry bap 28 April 1816; Frederick bap 18 January 1818; William bap 19 October 1819; Julia bap 27 June 1824; Caleb bap 26 November 1826; Charlotte Waters Mitchell bap in Rye, 24 March 1830. William the father seems to have left a will dated 13 May 1871 [Ancestry National Probate Calendar].
Mary, John and Sarah’s parents were William Mitchell and Elisabeth Milton.
William Mitchel was baptised (High Halden, 28 June 1772) and Elisabeth Milton was baptised in Tenterden, 12 March 1775). They married at High Halden 4th April 1793.
William Mitchel (bap 1772) was the son of William Mitchel and Susannah Duvran who married at High Halden 15 August 1768.
As well as William they appear to have had at least 2 other children; James (baptised High Halden 22 May 1774) and Frances, baptised High Halden 18 October 1789) and. [Note here that William and Susannah must have lived elsewhere and had other children between 1774 and 1789].
James Mitchel (baptised 1774) married Hannah Shoesmith in Smarden 13 August 1807. They had at least one son, James, baptised Smarden, 12 June 1808. [See my post 44 for other possible children].
James (bap 1808) is presumed to be the James Mitchell of the 1871 Eltham Census. This would make him the cousin of Mary, John and Sarah and the ‘first cousin once removed’ (I think!) of William Brook of Eltham. ‘Uncle’ seems a far more satisfactory description!
[Note that there seems to have been another Mitchell family in Smarden at the time as there is a James Mitchell bap Smarden 1824/1826 in the 1871 & 1881 censuses – RG10 Piece 1032 Fol.122 Page 44 & RG11 Piece 1029 Fol.61 Page 43].
Sources are mainly Family Search and FMP’s Kent collection of parish records.