18% feed should be pretty good, but see if giving 20% makes any difference.
Sometimes picking/plucking can just be a bad habit.
I would not treat with Ivermectin unless you see mites.
Permethrin based poultry dust or sprays are more commonly used to combat lice and mites on the birds and...
I don't see how antiseptics will prevent feather loss due to picking.
Look them over for lice/mites to be sure they aren't aggressively grooming one another of bugs which will damage the feathers.
I see broken feathers and plucked out places. Sometimes this is just a bad habit from one...
Looks like scabs from picking and some feather plucking going on.
Check them for lice/mites.
The white spots looks like debris that has accumulated in the nooks/crannies of the comb. Pop those out and apply your cream.
If you feel you need to apply an anti-fungal cream, you can use...