I have some verified information on my GGrandmother Sophie Cowan (nee Duffy)
1. Marriage cert 1879 to James Cowan (her father is Michael Duffy, occ. gardener)
2. Baptism details for her children list sponsors as Mary Anne, Catherine and Bridget Duffy (possibly sisters?).
3. 1901 census has Sophie and family living in upper Buckingham street. Her widowed sister Catherine Meehan and son are living with them. Both sisters say they were born in Co. Dublin
4. Catherine Meehan (nee Duffy)s 1885 wedding certificate has her father as Michael Duffy, occ. gardener.
5. Death cert for Sophie Cowan 1903 age 45. Informant Mary anne, daughter. She was supposed to be 45 in the 1901 census too so I hope this is the correct person.
This is where things started to get a bit difficult

I looked on RootsIreland for a Sophie Duffy born 1856-8. Only 1 match came up within 5 years either side of her possible birth year. The parish was Clontarf. The father was Michael and the mother was Catherine monaher. RootsIreland had 3 baptisms with the same father's name and the same or similar mother's name in the same parish. Mary Anne 1853, Bridget 1854 and Richard Joseph 1859. I couldn't find Catherine.
I thought if I could find a marriage for one of Sophie's other possible siblings with the same father's name and occupation it would help me confirm that I was nearer to confirming I had the right people and therefore I could be sure about Catherine Monaher as the mother. Unfortunately, the only marriage certificate I could find was for Richard Duffy to Bridget Conlon 1884. On the certificate Richard's father is Michael but he is a shoemaker not a gardener.
I'm hoping that someone can look at the information with fresh eyes and either tell me that I have been following the wrong family (I hope not) or point me in the right direction to find more of Sophie's siblings or their father Michael.