Hi Sarah,
Thanks for your pm, glad that's the right marriage even with the different surname.
The next thing to do is to order that certificate, which should clear up a couple of things, hopefully. It should tell you their ages, occupations, addresses, and fathers' names and occupations, and whether the different surname is because of a previous marriage or not.
Then you'll be able to find their parents' marriages, find them in the 1901 census and then you can work backwards through the census without too much more expense, but that marriage cert is a must, and will cost £7.
You can either order it directly from the GRO (giving the reference details I gave you) from:
http://www.gro.gov.uk/gro/content/certificates/or you could order it from the local register office, Hackney's is
The Register Office, The Town Hall, Mare Street, Hackney, London, E8 1EA.
Tel: 020 8356 3000
E-mail: registrars [at] hackney.gov.uk - (exchanging @ for [at] )
When you have that, please come back and post the details, (intrigued to know about the name change) and we'll try to help you further.
Kind regards,
Barbara
