I like to use Rooster Booster Multi Wormer (I get mine here:
http://www.abetterchicken.com/product/50101 ) which is a feed additive and easy to use. It is effective against 3 types of worms (round, capillary and cecal) and has no egg pull time as it is poorly absorbed by the gut and therefore not passed into the eggs. Since it's licensed for use in egg layers, the directions are right on the label on the container.
It will not do anything about external parasites. I use Permethrin Poultry Dust for external parasites which has no effect on the eggs (unless I guess you dusted it over eggs). You sprinkle on the birds (dusting well into the feathers) as well as spread it around the nest boxes and house. I sprinkle the dust on the floor of the coop and then put the bedding over it. You can get it at the feed store or simply google Poultry Dust. I've seen it on
Amazon (but not the best price there).
Ivermectin/Eprinex will indeed work on a host of worms and external parasites. I would add that it is well absorbed systemically (that's why it's so effective since it is transported throughout the body) and I personally would not eat the eggs during the dosage period. It is not licensed for use with chickens in the US so you won't find it in a chicken formula, however, as WalkingOnSunshine stated it has been used off label as such for some time. Usual withdrawal period for those types of wormers is 14 days from last dose meaning if you dose once then dose again in 10 days (frequently done), you should pull eggs for a total of 28 days.
I'm not seeing evidence of lice or mites from your one photo...your one bird looks like over-mating damage with also being picked on by another hen. Chickens will pick on anything that looks red. Some No Pick ointment will help with that, or put a hen apron on her to protect her until her feathers grow back in.
Here is a good website to learn about what to look for in extermal parasites:
http://www.the-chicken-chick.com/2012/08/poultry-lice-and-mites-identification.html
I agree a number of your birds are molting, and with shorter winter daylight, you will see quite a drop in egg production. Getting 3 to 5 eggs out of what, 10 hens?, would not be unusual for molting in late fall. My rule of thumb as I don't add lighting to my coop (burned one down that way) is 50% ratio of eggs to birds during winter especially with molting, and about 70 to 80% ratio in summertime.
You definitely have some Easter Eggers laying as the green/blue egg is from one of them. Your Buff Orpington or the Delaware mix is laying the light tan egg, and one of the production reds or red sexlinks the darker red brown egg.
If you would like a good dual purpose bird for laying and meat, New Hampshires are really good for that as well as Buff Orpingtons. I mix my flock so that I have better winter layers versus general layers. For winter laying I've added Delawares and Wyandottes and will be adding Buckeyes (although I've not tried them yet so can't attest). For general good layers, it is hard to beat the Red Sex Links and Black Sex Links.
I got a Silkie to brood for me, and it is a lot of fun to do so...plus it frees you from heat lamps and inside brooders...the hen does all the work.
Nice little flock. Great idea to buy all from the same farm. Always be careful when you add any other birds to this existing flock as older birds inevitably bring disease or parasites. Any new birds should be given at least 2 weeks quarantine away from your existing flock. Babies (chicks) should be raised until at least 8 to 12 weeks away from your existing flock to build their immune systems before being exposed to the older birds.
Good luck with your new farm.
Lady of McCamley