In terms of tracing Abraham back further, have you traced his marriage to Louisa? She was born in London so with any luck they will have married in England. Do you have her maiden name (from e.g. the birth certificate of Moss or one of his siblings)?
NB I see that they already had baby Benjamin before the 1841 census so they may or may not have married during the period covered by civil registration (1 Jul 1837 onwards).
His likely birth: Benjamin Abraham BENJAMIN, Jun qtr 1840 Whitechapel 2 506.
No, I don't yet have a birth certificate for any of the children. Was about to order
Adelaide Benjamin
Year of Registration: 1848
Quarter of Registration: Apr-May-Jun
District: Whitechapel
County: London, Middlesex
Volume: 2
Page: 5[79]1 .
I'm not sure but it seems the most likely. This should give me more information hopefully wouldn't you agree?
Thank you!
Alex