I wonder if the song you're thinking of is the "Ballad of Knocklong"? It doesn't say anything about in pairs up the stairs as far as I can remember, but it was about the rescue of Sean Hogan from the RIC by Dan Breen and Sean Treacy at Knocklong train station in Tipperary in 1919. I have only heard it sung once, by an IRA veteran who was 103 when I met him, so it was quite hard to make out most of the lyrics.

"The evening it was falling
As at last the train sped in
...... Dan Breen and ...
...Our courageus heroes
It did not take them long
And the rifles echoed true at the station of Knocklong

Oh King George's pampered hirelings
........
But the bravest deed of all
And it did not take them long
Was the rescue of Sean Hogan at the station of Knocklong"

I wish I could provide more lyrics but I could only catch fragments from the tape I made. Maybe these lyrics will help you to get a fuller version of the song from someone else.