Looking at the rules.

[Amak]

What does it mean with every other profile has to die? The second file you click?

[natknut]

it might help if you know how that english phrase works. One lives, next dies, one lives, next dies.

[Oak]

If taken literally, yes, like natknut said, you would mark one to live, then another to die, then another to live, and so on :)

[Oop]

Does it refer to the order you mark them, or to the order they lie on the table, or just generally to a half of the bunch? Judging by common use, each interpretation is valid for the phrase.

[Oak]

Generally half of the bunch. There's a also a plot-specific reason why Fate asks you to do it like this which I won't spoil here.