Hello Everyone and thank you for all your help. I still don't know if my Donnellys are related to the Peppard/Donnellys yet. But I do have a little bit of good news. I found my Donnellys on the 1901 census. They were living in 32 Upper Clanbrassil Street and I have found the names of my grandads brothers. However, as they are called Patrick, James, John and Michael, I'm finding it difficult to get a lead on them.
I checked in the Guinness Archives and found my grandad's record. They had a copy of his Birth Cert (oh joy!!!) and his mothers maiden name was Ann Callaghan. So now I have another piece of the puzzle. He had joined the Royal Dublin Fusiliers in 1909 and was posted to India (hence the reason why I could not find him on the 1911 census). I have since discovered that he was based in Ahmednagar Fort in India for the 1911 census and that he was demobbed in 1919/1920. The Guinness record mentioned that he had taken part in the 'European War', but did not list any particulars. Unfortunately, his military record was one of the ones damaged/destroyed in the Blitz, so no joy there.
I have posted on the Royal Dublin Fusiliers Website to see if anyone can give me information on the first batallions movements during the 14/18 war - so fingers crossed.
Again, thanks for all the great help and assistance given.