The one with pink legs could be, but the one with slate legs is probably a Phoenix bantam or a Dutch bantam. Hatcheries tend to sell bantam assortments to retail stores, so you can get anything unless they are in a bin marked as a specific breed.
I see no reason to doubt it is a buff Cochin. Could always be some kind of hatchery hybrid, but it doesn't match for any other pure breed that I know of.
Very perplexing. The comb and wattles are huge and very red for 15 weeks, even for a male. But I see no other sign of it being male except for the large, masculine looking head of the bird. I'm gonna agree with AinaWGSD that it is a quick developing pullet. Let us know how it turns out.
Most of the things you listed are not gender specific. Behavior is not a good indicator at that age.
But the raised comb at so early an age, the larger size and the thickness of the legs could mean you have a cockerel. I wouldn't say it is definite yet, though.
Keep watching the comb. If it...
Maybe lemon splash or buff splash? I am not sure. It's probably just a mix of colors and doesn't follow a specific pattern.
Silkies are difficult to tell gender with. It usually takes a long time. Comb size is the best indicator, so if it shows a raised comb at this point it is probably a male...
I am still not seeing strong indications of male specific feathering on this one, and it is very late in the game. I think it could be a pullet with a damaged ovary. It makes no practical difference except that if that is the case, it won't be able to fertilize eggs or lay them.
IDK, this one...
They are similar to speckled Sussex. The chicks are variable-- some are yellow, some with a bit of striping, and some with darker striping. It could still be something else, but there's a chance it is a Jubilee Orpington.
Maybe a silver Deathlayer rooster. I guess he could be Campine x white Yokohama. A good shot of his comb would help determining what type it is, and that should give the answer. Or at least help.
But as far as titles go for color varieties, birchen is silver based and brown red or copper is gold based. Birchen is used as an umbrella term in genetics. That's how I learned it, anyway.
She's not blue copper because there is no copper in her plumage. But she could be blue birchen, a similar pattern where the copper is replaced with silvery white. Or she could just be a barnyard mix. I would judge by egg color once she starts laying.
He is a blue wheaten Ameraucana cockerel. As far as niceness goes, individual personality is more important than breed in determining behavior. That said, I have not heard of any aggressive Ameraucana roosters. If he's well behaved now chances are he will remain that way, but really it is a wait...
Pearl Onyx are Mystic Onyx, which are a mix with Silkie involved, crossed with white Leghorn. I saw nothing saying they could be sexed using skin color. There are now several of similar hybrids sold under various brand names by the different hatcheries.