There are at least four approaches to finding your Morgan relatives who remained in Ennis. Others on this forum might have more ideas.
Browse through the 1901 census of the various Ennis census districts on the Clare Library website and note the numerous Morgan family clusters that were resident there at that time, i.e. possible relatives of yours and also possible ancestors of Morgans still living in Ennis.
Note the Morgans in the Index to Biographical Notices 1935-1985 on the Library website at
http://www.clarelibrary.ie/eolas/coclar ... ionm10.htm and see whether you can obtain copies of death notices, obituaries, etc. The latter often contain lists of family members, e.g. those who attended a funeral, with their relationships (e.g. "uncle of the deceased").
Note the numerous Morgans in the Ennis National School Registers 1898-1952 at
http://www.clarelibrary.ie/eolas/coclar ... rname4.htm and see whether they give any clues as to family clusters which stayed behind. There may be children who were mentioned in letters which your GGG wrote.
The Eircom phone book lists 5 Morgans in Ennis (see
http://www.eircomphonebook.ie/search/ennis/morgan.html ). You could phone them and see whether they know anything of ancestors who emigrated to Australia. Don't snort with derision. I've tried this cold-calling and it is remarkably successful. Sometimes those who stayed in Ireland have retained letters from the family members who emigrated but have never bothered to trace them to the present day families in Australia, USA, South Africa, etc.
Paddy
P.S. Recently the Clare Roots Society surveyed the Drumcliffe cemetery in Ennis - a very substantial undertaking which was completed in a remarkably short time thanks to strict project planning and execution - and I have been told that the following Morgan headstones were found:
Morgan, Delia d. 16 Jan 1978
Morgan, Patrick (Pappy) d. 23 Dec 1983
Morgan, Michael No date
Morgan, Evline No date
No address given.