I'm not saying this is the case with you and your birds but, this is the time of year when respiratory infections usually show up when people close up their coops and runs for fear of cold.
My coops have huge open windows on both East and West walls allowing the wind to blow right through. In decades of chicken keeping, I've never had a bird with a respiratory issue.
A brahma never needs protection from cold unless it is sick. You may now need to bring it into a warm space. The problem is most likely a virus and will need to run its course.