Hey Roberto, nice to see you posting work! First of all, you have great rendering technique with pencils, it really brings out the details of your characters. I do have a few thoughts on your first 2 ladies-
Pirate girl- she has some super-strong looking abs…maybe a little too much bulging? Otherwise a very good character.
Space girl- Great details on the suit althought her hips do not seem to have equal size/weight. Her left hip should stick out a bit more. Also, for all the space gear she is wearing she looks very skinny.
One other thing, you might try showing the girls in different poses that help distinguish them from one another.
Anyway, I love the idea…looking foward to updates sir!