Hi Val welcome to Rootschat
I'm afraid your information and dates don't match to Capability Brown's family. The tree itself doesn't really make a lot of sense dates wise at the crucial part where it tries to make a link with Capability's son Thomas and Mary Elizabeth's father Thomas.
'Thomas Brown died 1820 (I have him born 1861 from a book on Capability Brown.) She had him down as Rector of Fenstanton, Nothamptonshire for 40 years. His son, Thomas Brown, 1857-1925'
I think you mean Thomas was born 1761 and died 1820 (I think actually 1829) in which case it would be impossible for him to have fathered a son born in 1857 called Thomas. The dates for the Rev Thomas Brown 1761-1829 of Fenstanton, the son of 'Capability' Brown are correct as is a birth year of circa 1857 for Mary Elizabeth's father Thomas.
This looks more like Mary Elizabeth's line of Browns in Lincolnshire.
Winterton is in Glanford Brigg registration district.
1901 census RG13 3103 folio 8
Low Street Winterton Lincolnshire
Thomas Brown 43 Head Married Florist Swaby Lincolnshire
Annie M Brown 45 Wife Married Whitton Lincolnshire
William Brown 20 Son
Charles Brown 18 Son
Mabel Brown 14 Daughter
Henry Brown 12 Son
Christopher A Brown 10 Son
Mary E Brown 9 Daughter
Archbald Brown 8 Son
Ernest Brown 4 Son
Violet Brown 2 Daughter
children all born Winterton
The family was in Winterton in 1891. Thomas was a gardener aged 33 born Swaby. His wife's name was given as Annie Maria. Eldest son was Frederick aged 11 born Winterton.
1881 census RG11 3286 folio 14
Low Street Winterton Lincolnshire
Tom Brown 23 Head Married Gardener and seedsman Swaby Lincolnshire
Annie Maria Brown 25 Wife Married Whitton Lincolnshire
Frederick Brown 1 Son Winterton Lincolnshire
So after his marriage Thomas was very consistent with occupation, age and place of birth.
1861 census RG9 2379 folio 11
Swaby Lincolnshire
Fredrick Brown 28 Head Married Gardener Burwell Lincolnshire
Eliza Brown 30 Wife Married Swaby Lincolnshire
Mary Ann Brown 7 Daughter Swaby Lincolnshire
Tom Brown 3 Son Swaby Lincolnshire
1871 census RG10 3322 folio 6
4 Haines Yard Spalding Lincolnshire
Frederick Brown 35 Head Married Gardener Burwell Lincolnshire
Alice Brown 28 Wife Married Weston Hills Lincolnshire
Thomas Brown 13 Son White Pit Lincolnshire
1851 census HO107 2110 folio 426
South Ormsby, Lincolnshire
Frederick Brown 18 Burwell, Lincolnshire, Servant Labourer
A strong possibility on the 1841 census is this entry, but either of Frederick's two marriages would confirm his father's name and occupation, as would Thomas' marriage for his father's details.
1841 census HO107 641/14 enumeration schedule 5
South Ormsby
Joseph Brown 40 Gardener
Mary Brown 40
George Brown 17 Gardener
John Brown 12
Frederick Brown 10
William Brown 5
Betsey Brown 7
Fanny Brown 2
all born Lincolnshire - adult ages (those over 15) are usually rounded down to the nearest 5 on the 1841 census.
1851 census HO107 2111 folio 484
Kidgate Louth Lincolnshire
Joseph Brown 52 Head Married Gardener North Willingham Lincolnshire
Mary Brown 49 Wife Married Market Raisen Lincolnshire
George Brown 26 Son Tead Dealer North Willingham Lincolnshire
Charles Brown 9 Son South Ormsby Lincolnshire
Joseph Brown 4 Son Swaby Lincolnshire
plus three lodgers
JOSEPH BROWN
Christening: 24 JUN 1798 North Willingham, Lincoln
Father: JOHN BROWN
Mother: ELIZ.
JOSEPH BROWN
MARY LOWNDS
Marriage: 28 AUG 1821 North Willingham, Lincoln
siblings
JOHN BROWN
Christening: 19 MAR 1797 North Willingham, Lincoln
Father: JOHN BROWN
Mother: ELIZ.
WM. BROWN
Christening: 06 DEC 1801 North Willingham, Lincoln
Father: JOHN BROWN
Mother: ELIZ.
ELIZ. BROWN
Christening: 30 SEP 1804 North Willingham, Lincoln
Father: JOHN BROWN
Mother: ELIZ
So the probable (you could prove the census entries through obtaining the necessary marriage certificates) 2 x great grandfather of Mary Elizabeth Brown was John Brown who was having children with his wife Elizabeth in North Willingham Lincolnshire in the late C18th early C19th, and the family background on censuses was one of relatively ordinary villagers.
Information from censuses on Thomas Charles Brown the son of the Rev Thomas Brown of Fenstanton and brother of Lancelot Robert Brown have already been stated in earlier messages
'Thomas Charles Brown was still alive on the 1861 census, aged 69, born Conington Cambridgeshire'and
Thomas Charles was married by his brother to Frances Page, 17 Sep no later than 1825, and in 1841 were living with children Frances, Augusta Marcia and Lancelot Charles in Somersham, in 1851 with the younger 2 in St Georges Westminster, and in 1861 he was living with his brother Lancelot Robert and etc in Kelsale.and
'have ordered the Wills etc for Thomas Charles d 2 Jul 1868 and his wife Fanny (Frances) d 22 Apr 1870,' 'Thomas Charles Brown died 1868 in Chelsea registration district.'Regards
Valda