When first feathering out frizzles can look pretty "bad". It is possible they're frazzle but I wouldn't worry too much yet. The chick with the bare shoulders looks like it may have had the down plucked by other chicks/birds. My frizzles at three-four weeks look much the same as yours but the feathers fill in over a short time.
Oh, thank you. I hope you are right. I was so upset when I saw the one especially with his bare shoulders. My red and white frizzle look fine, but all the black, including the one that is regular, are sketchy with feathering.