I think your suspicions are correct. The body shape, tail shape, and comb of the 1st bird all look Leghorn. The 2nd and 3rd birds appear to be white rocks, but the 3rd is a cockerel.
I'm leaning cockerel because of the more flamboyant pattern and redder comb, but not completely positive yet. At 10 weeks, it's getting close to the time you can start seeing male vs. female specific saddle feathers, but keep in mind that EE patterns can be deceptive to your eye. The pattern...
I agree that those all look like pullets. I have a standard cochin hen that tries to crow (even though I also have a couple of roosters). She doesn't have a true multiple-syllable crow. It's more like an "AARRGH", which is tons of fun when she does it right by my ankle as I'm putting out feed...
Caveat to the comments above--the sex-link color is only valid for the first generation (chicks from using a red--usually RIR-- rooster with white hens). 2nd generations (chicks with red sexlink parents) won't be sex identifiable by color.
Either the comb and wattles will continue to grow and he'll start to show black feathers on his breast, or she'll stay the pencilled pattern and the comb and wattles won't grow much more until she's close to laying age.
The one in this thread apparently turned out to be a rooster: https://www.backyardchickens.com/threads/sexing-6-week-old-partridge-cochin-bantam.1086554/
Looks pretty similar. I'd give it a couple of weeks and see how he/she develops.
Honestly, I think Dutch and OEGBs probably get mixed at some hatcheries. A couple I've had have had a mix of red and white on their earlobes. They're pretty similar in size and stature (at least the ones I've seen, which might have a shared heritage, lol).