I
may have found the correct Robert Blair's family but bear with me because it's a bit complicated.
Starting with the marriage (1886) of John Farrell & Ellen Blair- her father Robert Blair a labourer and one of th witnesses a William Blair.
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1886/10848/5960957.pdf1901 and 1911 census records for the Farrells give Ellen as born c1867 but I think she was a little bit older than that.
I went through details of Farrell children hoping Ellen's mother might have been informant, etc. but no such luck. Then started looking for Robert Blair and William Blair in the area- found a few which I made notes on but nothing to confirm a link at that point.
Then, I found an online tree- turns out it's incorrect but did provide clues and link to Blairs I've already made notes on. So, here's the gist of the incorrect tree-
Ellen's father Robert Balir died c1863, a half-brother Robert Blair (no date of birth but wife c1841) married 1863 Eliza Hughes & one other un-named woman.
Next post is my version (with sources).