Hi Tammie, is there perhaps a mix up in the information that you have been given.
The 1871 census index is a bit confusing as it gives Fannys husband as William.
Josiah Walwyn born 1841/2 married Fanny Siviter born 1846 in aston 1869
in 1871 Fanny age 25 and her daughter Martha age 11 months are with her mother in law Elizabeth in Wylde Green
Elizabeth is a widow and also living there is Josiahs brother William age 19 b. 1852 unmarried a Railway clerk and 2 more grandchildren who obviously belong to another son Alice 8/Abraham 5 .Having searched the census records I cannot find Josiah.
1881 census has
36 Vauxhall road,Duddeston
Josiah Walwyn age 39 Joiner
Fanny age 34
William john age 9 (he died in 1886 age 5)
Martha age 10 is with her grandmother in Sutton.
In 1891 Fanny status married is living with her son in law and daughter william and Martha Betts in Sutton.
No sign of Josiah,he died in aston 1899 and in 1901 Fanny ,widow living in Sutton.
1861 77 Vauxhall Road Duddeston
William Walwyn Railway clerk
Eliza wife age 46
Josiah age 19 Builder and joiner
John age 17
Francis 15
William
I have found Fanny Siviter b. birmingham 1846 September qtr but have been unable to find her on census.