Okay, thanks. I can't think of anything else they can be other than just long, skinny robins with possibly a leucistic individual in there. American Robins have white undertail coverts, broken white eyerings, and orange breasts and they can be brownish above and, like all birds, can stretch themselves out and flatten their feathers to look long and skinny. The only thing that does not seem right for robin is pecking at the ground, but you didn't say whether they were doing that constantly or not.
My other options were:
European Starlings (juveniles)
Red-winged Blackbirds (females or juveniles)
Eastern Bluebirds (females of juveniles)
All of these gather in numbers on lawns, but they all don't quite fit your description.