Are these hens or one is different from the other? Also, what breed are they?

[Tookie]

I heard most of the single comb chickens grow combs and wattles from a very young age like after 5-6 weeks. But this one got after 2 months and has a single comb too. Is it possible that some single comb roosters develop their combs and wattles very late compared to the ordinary ones? If it wasn't about the voice change, I wouldn't have got in confusion. It's 50-50 at this point.

Yes, its possible. He may just be a slower developer.