trying an alternative angle ... probably an extreme long shot ....I had a look for deaths for the name of Mary Dempsy/Dempsey on the BMD Index after 1890, and of an age that might possibly be sister to your Edward - assumes of course that this Mary still lived in Co. Lonford when she died etc.....
Three civil registration districts covered the county, Ballymahon*, Granard* and Longford, the first two covered parts of other counties as well as Longford, and the third was based in the the County town also named Longford.
By far the best possible match is this one :
Name Mary Dempsey
Event Type Death
Quarter and Year Jul - Sep 1906
Registration District Longford
Age 84 (est. year of birth 1822)
Volume 3 Page 117
Death certs dont include family information except sometimes if the informant is family, so might be difficult to be sure if this is a connection, but if your've feeling lucky it might be worth splashing out €4 for a research cert ..