Hi both and welcome to RootsChat Historygirl  

The 1881 census shows Sarah born in Scotland,so maybe they were married there? 1871* has her birth place Berwick on Tweed. Do you know her maiden name at all - off one of the children's birth certificates, maybe?  

*
1871RG10/148 26 49
Marylebone, London William Crook, head, 40, Pianoforte Finisher, b. Bucks Eaton 
Annie, wife, 32, b. Berwick on Tweed
Annie E, dau, 8, b. London 
Alice, dau, 2, b. Middlesex St Pancras
Catherine, dau, 7 mo, b. Mddx Marylebone