Mrs. Foghorn Leghorn, I hate to steer you wrong, but...
the pics you posted look like hens to me. My little cockerels have much redder and larger combs than that. Also, I can't see their legs real well in those pics, but the legs look kinda thin to me? Again, my baby roos have thicker, longer legs. If yours will be 4 weeks old this week, I'm sure in another week the comb will tell the story. Wattle development in mine is almost even, with the roos having wattles that are only slightly more developed.
Also, keeping your hens for eggs? Of course you can! That's what their for, ain't it? Brahmas are considered dual purpose birds, but being so slow to mature aren't really all that great for meat. Mine will be 5 weeks old on Wednesday, the 14th. Ever single day that passes it becomes easier to tell the roos from the hens at just a glance.
Coloradochick, the hardest ones for me to tell apart at this age is my buff brahmas.
Edited to add this pic of Zeus when he was 4 weeks old, for comparison to yours.