Sue Do yu have a copy of the birth certificates? As Margaret was born in 1911 you could get the census for the address on her birth cert. Another item would be email Belfast Library Local History Section for a lookup of street directories. William may be listed under the surname section or if you had a street address they could check that way. I have found that a person may not be listed in both sections. I have a family member that is not listed under the surname section but is listed at an address. The ladies may not have gone to London as there was work in the cotton mills of Lancashire and Liverpool is a crossing point. Also take in to consideration the war years. Glen Alderson