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The Blandford registers have several baptisms for children variously listed as children of William and Martha Brown, or William and Martha Ann Brown (Elizabeth Ann, 1863; William, 1869; Ellen, 1872; Emily Jane, 1874).
The 1881 census lists William and Martha with William, 14; Ellen, 10; Emily, 6.
The 1871 census lists William and Martha with Sarah Jane, 10; Charlott, 7; Maria, 5; William, 3; Frederick, 1.
Freebmd has the following marriage:
Dec 1861 Blandford Forum
William Brown
Martha Ann Myall
In 1861 William Brown is a lodger next to Martha A Miles and her family.
Apart from London being a long way from Blandford, and several years after Sarah Jane was born, the banns for the 1868 marriage list William's wife as Mary Miles.
I can give you fuller details of the census entries and others, if you don't have access to them.
Richard