There is fast and slow feathering genes, unfortunately I am only knowledgeable in color genetics and not much else so I'm not entirely sure how they work!
Not a deathlayer, just looks like a small barred colored mixed breed :D the small comb means hopefully it'll be a pullet for you. Best of luck in her recovery
In some cases females will feather in faster than the males. More of a wives tale/rule of thumb vs an exact science, but can be an early indication of cockerels
Americana is the word they use! It's unfortunately meant to trick people, it's a purposeful misspelling of Ameraucana. Americana = Easter Egger or EE for short as you'll see many people use :D
Yes these are your boys! :D and from TSC they're not technically mutts/mixed breeds but they would be called Easter Eggers (bred to resemble ameraucana but much more common, non standard colors and bigger range of egg colors)
#1 just looks like a backyard bantam to me, where did you get the roosters from?
#2 it's not a great photo but I'm going to say Cochin based on body shape?
#3 assuming he is as small as he looks I'd guess old English game bantam mix or just barnyard bantam
#4 based on comb I'd guess Easter...
Maybe they're just feathering in slowly? I will try giving him a few more weeks to see if maybe they just have a small beard. There's always going to be a little bit of variation with genetics, fingers crossed you weren't scammed or anything, pretty birds!
Wing feathering isn't always accurate, and looking at feathers alone at this age isn't usually accurate either. The hackle and saddle feathers will come later, the large red comb and wattles indicate it's a cockerel, sorry.