I see Joseph and Amy had two children baptised in London - Sarah (1829) and William (1831).
Amy Crossman (presumably a widow) was married to James Saywell on 4 May 1834 in Hadstock, Essex.
1841 census - Duck End, Finchingfield, Essex (HO 107/331/17, f 11, p 16)
James Savill, 28, Shoe M, Y
Amy Savill, 30, Y
Alfred Savill, 5, Y
Thomas Savill, 3, Y
Sarah Crossman, 12, N
William Crossman, 10, N
The 1851 census suggests Amy was born in abt 1802 in Saffron Walden, Essex. There is a baptism in Saffron Walden for Amey Tyrrell, 12 Jun 1803, dau of James & Sarah Tyrrell.