I am still searching the above, but now have discovered another relative you might be able to find any records for Maria Johnston (daughter of Robert H )born 1839 Rockfor(d)t Bridge, Westmeath. She came to England 1861. Marriage 1867 to Frederick Gibbs. Cirencester, England.
Maybe she was illigitimate, as seems strange now we have found Robert had this daughter until now unheard of and he didn't marry until 10 years after the birth of his 3 sons ?
Maybe a wife still alive at the time in Ireland. Any help
please most welcome...going to Canada next week meeting up with some Johnston relatives, so exciting time. Jill