When did your great-times-three grandparents die, and where did they die? Did they die within two years of each other. There were cholera epidemics during the mid-19th century, not only in the UK but in the US and Canada, and cholera, influenza, cancer, etc. didn't wait for an epidemic to kill. There was tuberculosis. Arsenic poisoning (the direct route through food and the indirect route from the dyes in clothing and wallpaper.) An accident? Overwork? (If your great x 3 grandmother had to raise her children and work to provide food and shelter for them, as well as do the housework, she might have worked beyond her strength.) Did your great x 3 grandfather work in the mines or in the factories? No safety precautions, and people did slowly die from their work environment. The farm wasn't so safe either. A restless horse, a muddy embankment, a river in spring-flood... all could result in a fatal accident.