Didn't I read somewhere that Jim Sheridan (the director of 'Brothers') wanted both little girls to "fall in love with Jake" (off set, that is), so their acting would be as real as possible?! After all, they love their uncle Tommy...
I don't remember reading that, but I think it worked:
I loved Brothers, too. I don't think it's at the top of my list just because Jake was underutilized. I think they could have done so much more. But I love the way he looks in it. Haven't watched in a while, so maybe I should reconsider
Also, those two nieces are 3.5 years older now. I wonder if they both still act. Pretty sure the older one does.