I put my guess on that one too as he was just so much chunkier when he hatched, thick legs and all, kids named him Steve. The small comb is throwing me, every other pic of a Rhody has a huge red comb at this age.
Hmm... And you have no other birds or neighbors with birds?
These are definitely pullets in my opinion. A Rhode Island Red cockerel that's crowing should at least have some more prominence in his comb signifying that his hormones are beginning to pump at this point. I'm not doubting you heard what you heard, however. Though very, very uncommon, pullets do occasionally crow even at this age. I had a Barred Rock bantam pullet crow at around this age, myself. Before her, I would have not even considered the idea. But she is now a 2 year old, egg-laying, no-longer-crowing hen. So I guess it does happen!