I'm not sure the writer understood what the original "The Lady or the Tiger", was about. The man was not choosing between the lady or the tiger, the man believed the princess would choose best for him and picked the door she indicated. The, as stated a few times in the original story, semi-barbaric princess was the one who had to make a choice between the lady or the tiger. It was a choice of either getting the man killed by the tiger so he would be in the afterlife waiting for her or if she would live the rest of her life knowing the man she loved would forever be with the woman she hated most. Being semi-barbaric, this would be pure agony.
Now the thing I don't understand about McDermott's story is why he made the kid who has to decide, ten years old. Sure he knows what evils his brother has done. And sure he likes the girl. But unless I missed something, I would think most ten year old boys, especially seeing how chummy these two were, would automatically save their brother over a cute girl. Why didn't the author make the kid older, at least a teen, and maybe already dating the girl. Then I could see more of a quandary.