Excellent photos.
I believe these are sparrows, not Indigo Buntings. If you compare these pictures to your bunting pictures, the buntings have a very plain face/head and dark wings with fairly faint wingbars.
This one has orange-y brown face with grey sides and back of neck with a dark crown. It lacks wingbars and has overall warmer colors than immature Indigo Bunting.
My best guess is an immature Swamp Sparrow, but it lacks the mustachial stripes, so I'm not completely sure.
/Thomas