Keeping in mind that ivermectin is a product mainly used to treat cattle and is off label for chickens, I hope you know that ivermectin's primary purpose is a wormer, it's secondary benefit is that it kills mites, but not chicken lice. Chicken lice do not suck blood. Cattle lice which are a different type of lice suck blood from cattle. If you're dealing with external parasites, you'll still have to treat the inside of their coops, nests and roosts...preferably using sevin dust and redusting in 7-10 days to kill nits hatched from eggs.
The dosings you have for your birds are good. Put the drops of ivermectin on the back of their necks, make sure it goes on bare skin so it can be absorbed into the bloodstream. It will quickly be absorbed. I dont recommend giving the eggs back to the chickens. This will increase the withdrawal time, additionally the wormer residue in the eggs will help build worm resistance against the product. Ivermectin will not kill cecal worms nor tapeworms, and large roundworms have been showing resistance to the product due to its overuse as a miteacide in chickens.