You're right on the money with you gender guesses. You don't really need any roosters unless you intend to hatch your own chicks, in which case one would probably be enough. You might get away with 2 since they've been raised together. That's really up to you. But I wouldn't keep 3. That's just...
THe blue one in the 4th picture is a definite cockerel. He's an Easter egger of some sort.
The mostly black one in the 6th and 7th picture is also probably a cockerel. This looks like a Wyandotte.
The taller one in the last picture is might be a cockerel, but too early to say with that one. I...
1, 3 are gold laced Wyandottes
2 could be a Marans or olive egger or black sex link, among other possibilities. Australorp is the most common breed of black chickens, but the chicks usually have white on their faces and chests, so I think this one is something else.
4 yes, you're right...