The OP is picking up hens so they're not from a hatchery. Any bird other than newly hatched chicks, even from reputable breeders with tested flocks could be carrying a disease or parasites so needs to be quarantined
Feeding, watering, handling, bedding changes, collecting eggs, etc..
It's a Black Penedesenca, my favorite breed and the one I raise. I can tell it's not the same. The penedesenca has a carnation comb. It and empordanesas are the only breeds in the world with a white earlobe that lay a brown...
Best advice is to quarantine new birds for at least 2 weeks as far from your flock as possible. Work your birds first each day and wash up after handling or working the new birds.
After that, free ranging together helps but then the trouble is that the new birds won't know where to sleep.