I got to the Stratford-Perth Archives today and found Ada (Scott) McDermott's obituary. No mention of siblings or children (simply says "Her husband survives.")
Although the Annie MacPherson home has a historical designation the archives has no records from it.
My next step is Hamilton Public Library for obits of the others.
Depending on what I find there I may write to England and ask for access to the records on compassionate grounds: it appears that Eliza and Ada died without descendants. These names will never been remembered.