First is a roo second is a pullet. Guess for right now.
On the black chicken, if the feathers at the end of the back right before the tail starts, start to come in very pointy and not round then that could be a roo. It is hard to tell from the photo if the feathers are pointy or if it is just the lighting playing tricks.
If these birds are 7 mos. shouldn't they be laying by now? If either of them is a hen? I have CM that began to lay in cold November and have been laying pretty good. If you suspect a hen and your other hens are laying and "she" isn't then, she either late or a roo, right?
Though I too would think the black cochin is a hen. There are many things that can affect a hens laying or not.
As for the non- crowing roo, seperate him for a time and if he's a roo, he'll start to crow. Nothing brings out a roos horns than when he's been seperated for a time. Course you could start having fights like Eric and Nick. They fight til there's blood and even through a screen/poultry wire door.