how old are they? also the 2 marans need to be treated for leg mites as would the rest of them and the likely hood that they have lice/mites in their coop/run is also high when you have leg mites
Probably need a few more pictures from different angles. Polish are difficult to sex. From the head shot, it looks like a hen. But in some of the pictures I thought I saw some saddle feathers coming in. So in that case it may be roo. How old are all the chickens? I can't tell on the marans from the angle of the pictures either.