Molting or Mites?

[Esshea]

I have a speckled sussex who had been losing feathers close to her vent for the past month. At that time I thought it was related to my roo over-mating with her as I didn't see any evidence of lice or mites. Well, rooster is gone and now 2 other birds have missing feathers around their vent. I have treated the whole flock with poultry spray and am going to treat the coop later today since our rain has passed and then retreat the flock.
My friend seems to think the chickens are just molting as it is the season for it. In your experience have you ever seen molting start around the vent first? I thought it started at the neck.

 

[sourland]

Any possibility that on of their flock mates is feather pecking/plucking.

 

[Esshea]

Any possibility that on of their flock mates is feather pecking/plucking.

I considered this but I've never witnessed any other hens pecking. I have 3 younger pullets that do their own thing and are quite skittish of my older 9 girls. The 9 hens get along great from what I can tell. Maybe I need to install a coop cam