one thing keeps distracting me...

I saw them as possibly being the "master" scarecrows, those that started it all. They're always there watching, luring people in with voices.
When the robbers get killed, they become undead scarecrows themselves. And the three scarecrows that kill the robbers seem to be the three men in the photograph, who also somehow became scarecrows. So it seems like a circle, people on the farm are being hunted by scarecrows and they become part of the scarecrows once they die (or the new batch if all the old scarecrows gets killed).
But all that had to start somewhere, the three scarecrows (including the breathing one) seemed to be part of that origin.

Otherwise, they worked nice as a mood piece. They gave a somewhat omnipresent feel to the scarecrows.

The Scarecrow isn't breathing, as Bill Wesley explains none of the Scarecrows that appear on the crosses had actors inside them, they were props and what appears to be movement or breathing is in fact a side effect from the wind. End of.

It's all a deep end.