km1971
thanks for taking the time to reply, I was hoping after reading your previous posting that you would see this.
I had been through FindMyPast & have done so again, the problem is I have no idea which Regiment they were in.  Checked all the Byrne/Burns/Byrns/Byrnes available & non of them seem to fit. There are so many Hayes & the only Mallon I found was discharged as unfit much earlier than 1870.  
I was hoping that as I found Hayes & Mallon in 1870 Belfast Street directory living next door to each other in Great Patrick Street that I had half cracked the problem & that it would be easier to find their marriage/children's birth records that would help me find their Regiment.  The other problem I have with FindMyPast is that I have no idea where they were born & that makes it difficult to narrow down the searches.
Ancestry hasn't proved to be any further help.  Any suggestions?
Are you able to confirm which Regiments were based in Barracks near Artillery Street around 1874 when Patrick & Edward were married?
Many thanks
VB