I need help tracing my Great Grandmother Ellen ALLEN birth and marriage details.

I have her death certificate (Tonbridge 1909 Dec Qtr, Vol 2a, Page 457) which shows she died on 28 November 1909 in 24 Norfolk Road, Tonbridge. The death certificate states she was 67 years old, wife of William CURTIS a Hawker, the informant was her married daughter E BAKER.

Ellen appears on the following Census returns as the wife of William CURTIS as follows:

1901 Class: RG13; Piece: 757; Folio: 124; Page: 10. Living at 21 Norfolk Road, Tonbridge. She is 59 years old born in Marylebone, Middlesex.

1891 Class: RG12; Piece: 681; Folio: 81; Page: 2. Living at 5 Lamberts Yard, Tonbridge. She is 49 years old born in London.

1881 Class: RG11; Piece: 914; Folio: 83; Page: 25. Living at 20 Victoria Road, Tonbridge. She is 42 years old born in Middlesex.

1871 Class: RG10; piece: 1953; Folio: 46; Page: 22. Living at 98 Cromwell Place, St Thomas, Salisbury. She is 30 years old born in London, Middlesex.

I have not found her in the 1861 or 1851 Census records as I am unsure of her parents names. Ellen's birth year for the above Census returns are shown as 1839, 1841 & 1842.

I have bought a copy of a marriage certificate (Gravesend 1876 Sep Qtr, Vol 2a, Page 658) the marriage took place in Gravesend Registry Office. However, I am not convinced that this is the right people although the ages are near enough, my reason being that William & Ellen had 4 chidlren by 1875 (William Curtis abt 1868 born Droxford, Hampshire (I can not find his birth details), Albert Curtis born 1 Feb 1871 Brown Street, Salisbury, his birth certificate confirms Ellen's maiden name as ALLEN, James Curtis born 1873 Salisbury & Emily born 1875 Salisbury), on the marriage certificate I have it shows William living in West Street, Gravesend his occupation Bargeman and Ellen living in Bunces Street, Gravesend. Why would they be living at different addresses, William's occupation according to Census 1861 is Agricultural Labourer, 1871 Labourer, 1881 General Labourer and on his daughter Mabel born 1878 in Tunbridge Wells he is an Agricultural Labourer.

Ellen's husband William CURTIS was born 20 Sep 1842 in Hornchurch, Essex (Romford 1842 Sep Qtr, Vol 12, Page 205) and he is recorded on the 1861 Census Class: RG9; Piece: 1072; Folio: 48; Page 6 aged 20 living with his parents Samuel & Elizabeth.

Any help that would enable to progress my family tree would be appreciated.