Hello Cormac,
I dont know if you uploaded the pictures in the way you numbered them in your post?
First bird is a Dunlin. Please note black patch to belly, everything is there.
Second birds are all Golden Polvers. Please note warm golden-buff sprengled upperparts and the right body-shape with a pear-shaped body, and a rounded head in the profile bird. I exclude the rarer two others just by location.
The third shows: Black-tailed Godwits (the larger birds), Knots (grey, larger, round body, short bill). The little bird among them is hard for me.
At first it seems too small for a Dunlin, but this is hard to judge. More, the bird doesnt shout Dunlin too me. But the reason is surely some kind of single picture effect.
I am puzzled, because I get the feeling that Little Stint isnt the right answer too. Do you have more pictures of this bird? I guess it might well be a pitfall-picture of a Dunlin, after I downloaded the picture. And I discovered one more bird, that might be a Dunlin, hiding just behind the mystery bird.
And after a third look, I think that a Dunlin might well be the best fit. But Nearctic vagrants must surely considered in Ireland? I hope for more pictures and comments!