Quick first sketch of the chronology here [now amended several times for extra information].
1839 (Dec qtr): Birth reg of William James Sewell, Holborn
1864 (16 May): William James Sewell marries Mary Ann Holmes, St Barnabas Finsbury (St Luke's district)
1869 (9 Jan): Birth of Martha Mary Ann Sewell (per baptism record). Possibly the same person as "Annie", 12 in 1881, but her birthplace given as St Luke's.
1869 (Jan qtr): Registration of birth of Mary Anne Sewell, St Olave
1871 (census): Family at Ernest St, St Pancras. Only child is 2 yo daughter "Mary E", 2 b Boro'.
c1871-3?: Birth of Annie A Sewell (17 or 19 in 1891, birthplace not stated)
1873?: Birth of Alice (Louisa) Sewell (Alice, 8 b Clerkenwell in 1881 - not found in 1891 unless she's the person enumerated as "Annie A")
1874 (5 Jan): Baptism at St Pancras of Martha Mary Ann Sewell, born 1869 ("of 9 Drummond St")
c1874-8: Death of Mary Ann Sewell (William’s wife)
1878 (9 Jun): William James Sewell marries Ann Grainger, Holborn (both "of 3 Queen St")
1878 (Dec qtr): Birth reg of Ann Sewell, Holborn ("Annette", 2 b Clerkenwell, per 1881)
1881 (Jun qtr): Birth reg of William James Sewell, Holborn (baptism record gives birthdate as Jan 1881).
1881 (census): Family at 9 Little Gray's Inn Lane. Children Annie 12, Alice 8?, Annette 2?, William J 1mo?
1881 (28 Jun): Baptism of Ann & William Sewell ("of 9 Little Gray's Inn Lane")
c1881-7?: Birth of Sarah Sewell (20 in 1901 but "32" upon marriage in 1919) Not found in 1891
c1887? Birth of Annie Sewell (14 in 1901) Not found in 1891 or after 1901
1889 (Jun qtr): Birth of Harriet Sewell, London City
1889 (Jun qtr): Annie Martha Sewell marries Frederick Buckthorpe
1891 (census): Family is at 29 Plough Court, Holborn. Son W 13, daurs Annie A 17, Harriet S 2.
1891 (22 Nov): Alice Louisa Sewell marries Arthur Edward Taylor, Christ Church, Southwark. Her father is named as William Sewell, Labourer
1893 (Jun qtr): Birth of Charles Henry Sewell, Holborn
1897: (13 Jun): Annie Sewell (18) marries Thomas Murray (18) at St Paul, Clerkenwell. Her father named as William Sewell, bookseller.
1901 (census): Family at 1 Sidmouth St, off Gray's Inn Rd. William (W. J.) is a bookseller. Children William 22, Sarah 20, Annie 14, Harriett 12, Charles 8.
1914 (12 Apr): Harriet Louisa Sewell marries Frederick Murray, St Philip Clerkenwell
1915 (Mar qtr): Possible death: William Sewell aged 72, Islington.
1919 (31 Mar): Sarah Sewell marries Richard Jones