Sarah, we seemed to have moved away from your original request for info on Martin Powham. I see now he died in Paisley, Scotland in 1950. Was his mother's name not known to the informant who reported his death?
With wife Kate McDuff, hopefully you have more details to follow up on. Looks like her ancestry will take you to Ireland on both her maternal (Brown) and paternal (McDuff) lines....
I see you have your tree on Ancestry. There are a number of trees on the family of Margaret Brown such as this one
www.ancestry.co.uk/family-tree/person/tree/19453904/person/823163758/facts These include death dates for Margaret's parents. As mentioned, their death certs should be on SP letting you work back to the next generation. In the main, Margaret's mother is showing as Julia Durnan (suggest with Durnan you search where possible with wilcards suchs as Dur* or Dor*).
On the McDuff side, we have now Terence's parents as James and Mary. Not sure yet on her maiden name.
Monica