I'm no expert on brahmas, but a couple of yours do look a bit dark to be a light brahma. I believe pullets should still have tiny pink combs by 3 months old - check the wattles too - they shouldn't be very big on a pullet of that age.
Here's some pics of my roo about the same age as your chicks (9 & 12 weeks) so you can compare his comb & wattles with your chicks. I have no idea of his quality - he was hatched from an egg I got on ebay:
He was 9 weeks old here:
These next two pics were taken when he was 12 weeks old - just after he started crowing.