Respiratory illness could be caused by any number of things, from bacterias or viruses to inadequate ventilation. Since it comes and goes, it's more likely environmental. Be sure to have lots of ventilation in your coop and also pay special attention to keeping the coop dry. The Faverolles' bare belly may be due to broodiness. They are very prone to brooding spells.

Is what I’m gonna say to the broodiness!
It’s been a broody spell marathon here the past 2 weeks..
