Hello, acky,
This what I have been able to find for your Benjamin Isaacs. It has been a bit confusing as the family does not seem to be so sure about the name for Benjamin's wife nor where they were born. There were clues that needed following thro' & searching, but the marriage at the end of the info gives one answer.
1901 census
RG13/199 folio 68 page 13
22, Arthur Rd., Islington, Highbury
Benjamin Isaacs age 66 Cab Driver b Mile end
Mary wife age 68 Nurse b Marylebone
1891 census
RG12/127 folio 14 page 22
42, Charrington St. St Pancras Somers Town
Benjamin Isaacs age 58 Cabman b Strand
Mary wife age 57 b Marylebone
Alice dau age 26 b St. Pancras
Jane Ward age 14 Don Serv. b St Pancras
1881 census
Rg11/348 folio12 page 19
129 Pentonville Rd., Clerkenwell
Benjamin Isaaca age 46 Cabman b City London
Mary wife age 45 b Middsx
George son age 16 b City London
Alice dau age 14 b ditto
1871 census
32 penton Place St James clerkenwell
Benjamin Isaacs age 43 Cab Driver b London
Elizabeth wife age 33 b St George's
Alice dau age 6 b Pancras
George age 3 b Islington
Mary Feist Mother age 67 W. Housekeeper b Durham
Katy Feist neice age 9 orphan b Brighton
1861 census
RG9/48 folio 65 page 32
7, Romney Terrace Westminster, St James Evangelist
Benjamin Isaacs lodger age 27 Gen Porter b Westminster
1851 census
HO107/1511 folio 129 page 3
St Paul's Covent Garden
head of house,
Francis Dawson age 24 Fruit & potato dealer b Hull Yorks
Benjamin Isaacs serv age 18 Errand boy b St Martin's
1841 census
HO107/716 bk 2 folio 8 page 7
Mount St., St Mary Whitechapel
Ester Isaacs age 50 Clothes Dealer born in county Y
Judith age 45 b ditto
Stephen age 20 b ditto
Aaron age 18 b ditto
Abbey age 15 b ditto
Benjamin age 10 b ditto
Mary age 6 b ditto
Could not find a birth record for Benjamin
Marriage
Benjamin Isaacs = ELIZABETH MARY Feist
Mar ¼ 1873 Holborn 1b 641
Death
Bemjanin Isaacs age 70
June ¼ 1904 Islington 1b 209
1861 census
RG9/593 folio 138 page 21
2, Boro' Gardens Brighton
Mary Feist age 56 W Upholsterer b Dorking
Ann dau age 19 Dressmaker b Surrey
1851 census
HO107/1645 folio 617 page 17
20, Grovensor Rd., Brighton
Mary Feist age 47 W Charing b Dorking
Richd son age 17 Porter b St George's Middsx
Elizabeth dau age 13 with her mother b ditto
Anne dau age 8 b Dorking.
The 1871 census showing Mary Feist being born in Durham is possibly a mistake bt the enumerator mis-hearing Dorking, & you can see where the confusion was with the name of Elizabeth Mary being Benjamin's wife.
The 1861 & '51 census showing Benjamin being born in Westmister are a bit suspect but on the 1891 census he has put Strand which is also in Westminster.
Hope this has all been of use,
Meliora