Hello
I got 2 light sussex chickens. They are "Twins" and 12 weeks old. I think it is one rooster and one pullet.
One of them got a bigger and redder comb "he" is also more dominant.
I may have to amend my previous statement... You may have two cockerels after seeing the tail of the "pullet". It has "cockerel type" sickle feathers coming in. Which is not a sure sign of not being a pullet. "She" may molt them out and not ever get them back, this does happen in some breeds.