Good afternoon Hielke
I am originally from Saltcoats now residing in Western Australia.
Go to http://www.threetowners.com/ select "Visit Our Forum", "Genealogy" and place your enquiry there.
In addition, e-mail localhistory[at]north-ayrshire.gov.uk (replace [at] with @) Attn: Ms Jill McColl offer your information and ask your question/s.
I have completed a quick internet search and offer the following without recognised proofs; ie. Birth, Marriage Extracts. Alexander (son of Peter Simpson) and Annie (daughter of John MacAdam / McAdam) married early-March 1920 in Ardrossan (a town adjacent to Saltcoats). It would appear that Sergeant A Simpson, along with a twin sister, was born late December 1920 in Saltcoats. In addition, it is probable that another younger sister was born February 1923 following by an even younger brother January 1926.
Kind regards.
Q98