Comb:
You're right they are hard to see, but I'm sure those are not single combs.
Probably rose, possibly walnut/cushion, don't really look like pea comb. I keep thinking I'm seeing a buttercup comb, but I think thats just the shadows messing me up--I have never heard of a black chick with a buttercup comb.
Dominques have rose combs, and I think that is the most likely breed. Dominiques grow barred feathers (black and white stripes), so you will see that soon if they are Dominiques.
Wyandottes have rose combs, but black ones are fairly rare. Barred ones and blue ones are pretty rare too. I think Wyandotte is the second most likely breed.
Sumatras have pea combs, but I think the combs look more like rose than like pea, so probably not.
Easter Eggers, Olive Eggers, Favaucana often have pea combs, sometimes have single combs. I don't really think those chicks have pea combs, and certainly not single combs. So probably not any of those breeds.
I think all the other breeds that have been mentioned in this thread have single combs, and I'm sure those combs are not single combs.
So I think you've probably got Dominiques, with a chance of Wyandottes.