Can you weigh one of them?
In general, bantams are about 2 pounds and under, most other chickens are about 4 pounds and up.
Based on the coloring, they could be Silver Duckwing Old English Game Bantam (one of the most commonly-available bantam varieties). If they are under about 2 pounds, I think this is the right answer.
If they are bigger than that, I can't find any common pure breeds that would fit their appearance, but I do find a few rare ones:
Silver Leghorns
https://www.mcmurrayhatchery.com/silver_leghorns.html
(Would lay white eggs, visible traits all appear to be correct)
Silver Phoenix
https://www.mcmurrayhatchery.com/phoenix.html
(leg color is wrong, but otherwise they look about the same. More likely for the one with a long tail and an upright comb, less likely for the one with a shorter tail and flopped comb. Would lay white or off-white eggs, but maybe not very many of them.)
I'm ruling out Silver Dorkings, because of the leg length and body shape, plus Dorkings would have an extra toe on each foot:
https://www.mcmurrayhatchery.com/silver_gray_dorkings.html
If they lay blue or green eggs, then some kind of Easter Egger (mixed ancestry, but almost certainly has some Cream Legbar in there somewhere, to give that appearance.)
If they lay dark green eggs ("olive"), then Olive Eggers (mixed ancestry, again including some Cream Legbar.)
If they lay brown eggs, then they're some kind of hatchery hybrid I haven't seen before, or some pure/rare breed that I've forgotten about.