If they have little sticky up tails, then those are probably female as the males tail feathers develop later
The Marans (French and English) are a brooding breed, and make excellent broodies in my experience, though I only keep a few, and don't set their eggs as I am trying to mostly breed it out of my line as far as possible.
I am afraid I know nothing about the French varieties, and in fact am going to see my FIRST EVER French Marans tomorrow
Mine are all the traditional English Dark Cuckoo type so of course that is where the markings come in. Do they have any evidence of feathers on their feet? If so they won't be the English type Marans
Mine are exceptional calm temperament, both with me and with each other, and have proved to be good layers. My young pullets are just starting to lay at mostly under 24weeks, the earliest was under 19 weeks
All the best
Sue