I may have found all four on the 1911 Canada Census. Edger and Arnold were in what is now Mississauga,Ontario.Margaret is married in Sakatoon to a Smith. Herbert was still single in Vancouver. Problem is there were three Herbert's so I don't know which one it is yet.
According to 1901 Canada Census for Brockville Ontario. Lillian's brother is listed as Lindsay L. Casselman. Just for some confusion.