Bald chickens

We have 1/2 a dozen happy and very productive chickens plus their cockerel, over the last month or so we have noticed that two of the hens have lost a substantial amount of feathers from the backs at first we thought it was just a molting process.
6 weeks on these two are still bald, is this case of these two being the cockerels favorite girls or something more.
What can we do to give them back there good looks?