Your Lennox family is on both the 1901 & 1911 censuses http://www.census.nationalarchives.ie
There are also 2 baptisms for Lennox children here http://churchrecords.irishgenealogy.ie
You might a couple of the Lennox boys listed in the 1939/40 Electoral Rolls here http://www.dublinheritage.ie/electoral/index.php
Do you live in Dublin? If so you can go the the Library in Pearse Street where they have Electoral Rolls up to (I think) 1963 & beyond.