Mag,
The 1874 marriage certificate states that both Peter Clarke and James McKenna were farmers. So you would expect them both to be in Griffiths Valuation (1856). The marriage certificate also mentions that both were alive in 1874. Patrick Clarke’s townland was Deigan on the marriage certificate which I think is the Dingin you found him at in the 1901 census. Griffiths lists Pater Clarke farming there on plot 2 which was a 13 acre farm. Today it’s off the R165 not too far from Kingscourt.
James McKenna is shown as living in Rakeevan. There’s no James McKenna there in Griffiths. The only James in the parish was in Corraghy where he had plot 4 a 23 acre farm. Corraghy is about half a mile east of Bailieborough.
Peter Clarke died at Dingin on 16.3.1887 aged 96. He was a widower and his son Pat was the informant.
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1887/06224/4781278.pdf
James McKenna possibly died in 1891 aged 80. There is a death with that information in the death indexes. Unfortunately the image isn’t on-line and so I can’t confirm it’s the right man. You would need to order a copy from GRO Roscommon to get the details.
This looks to be that Corraghy farm in the 1901 census:
http://www.census.nationalarchives.ie/pages/1901/Cavan/Bailieboro/Corraghy/1053217/
The birth certificate for Ellen on 10.4.1899 tells me the mother was Mary Sheridan.
https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1899/02040/1781631.pdf
Mary Sheridan & Frances McKenna married on 25.11.1874. His townland was Rathkeevan (Rakeevan) and his father was James, a farmer. So I would guess that Francis is Anne’ McKenna’s brother. I am not quite clear why the family appear in the records for both Corraghy and Rakeevan. Farmers tended to stay put.
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1874/11254/8127422.pdf
Statutory birth registration only began in Ireland in 1864. Patrick & Anne were born before that and so you will need to rely on church records to trace their births/baptisms.
Corraghy and Rakeevan are both in Bailieborough civil parish and Killane RC parish. Killane’s records start in 1835 and are on-line on the nli site.
https://registers.nli.ie
So you may find Anne McKenna’s baptism there, plus that of her siblings. Likewise Enniskeen is in Kingscourt RC parish and their records start in 1838 (with some gaps). You may wish to search them for Patrick’s baptism and that of any siblings.