The shape at the end of the saddle feathers (and other parts as well) will be shaped differently based on gender. Roos will have very pointed ends and the girlies have very rounded feather tips. A good way to "train" yourself to use this method of sexing chicks is to spend a little time...
The "barred" chick in the foreground of your picture has eyes shaped like a marans. Don't be surprised if that's a cuckoo marans rather than a barred rock.
The 2 white ones look like white rocks or some derivitive of white rocks. I say that as white rocks have been used as a base breed for many of the production type broilers and they can look very similar. Take a look at Cobb 500 and Cobb 700 chickens and you will see how close they look to your...