I find the Robert John BROTHERSTON born 8 Dec 1890 son of Andrew and Agnes had siblings - William born 1883 died 1956 Dummer tp Peterboro co Buried Warsaw.
Twin sisters born 6 July 1892 named Annie and Mary at birth parents resided Smith Twp Peterboro Co.
The brother William s/o Andrew BROTHERSTON and Agnes RICHARDSON married Margaret McCracken 25 Nov 1920 intended to marry in Peterboro they were both 37 she d/o Robert MCCRACKEN and Euphema SMALL. Both witnesses and minister were from Lindsay.
There is a tree at ancestry that has William and Margaret on it - titled McCracken Landing owner Heather ZAK.
Perhaps a descendant of William BROTHERSTON would know something more abt his brother Robert John.
The genealogy society for the Peterboro region might have something on the family. I think its Kawartha Lakes Genealogy Society its under Ontario Genealogy Societies.
Also the Delafosse Branch of Peterboro Library houses lots of genealogy stuff so they might be of some help.