I do not think there is anything to be gained from continuing to search for the marriage record, and better to proceed with the idea that they were not married.
That enables you to consider other possibilities. Where couples were having a family, but there is no marriage record to find, it was likely because one or both were already married.
If Margaret is 27 years old at birth of first DUNNE child that would be a bit older than usual for that time.....just something worth noting.
I am assuming that you are looking for the marriage record because you are researching the origins of John Edward DUNNE and Margaret KELLY?
Reading from the birth certificates you have please, and using one for which father John Edward is the informant, can you give any information he gives about himself - age, birthplace.
Reading from the birth certificates you have please, and using one for which mother Margaret KELLY is the informant, can you give any information she gives about herself - age, birthplace.
If any of the certificates do not have mother or father as informant, can you name this informant please.