You dont give chicks ivermectin that young. It'll have adverse effects on their nervous system, besides, chicks dont get worms that young and mites should not be an issue if they came out of an incubator. If they were hatched by a hen and the hen was infected with mites, then yes, it's best to dust both the hen and each chick with permethrin dust.
I suspect that you're dealing with cocci and the corid isnt having any effect controlling it.
You're going to need a sulfa drug to kill the cocci. With an outbreak this bad, you're going to need a prescription from a vet to get sulfadimethoxine and treat all your chicks. You'll need enough to treat your chicks for 5 days. The vet will provide you the dosage.
To slow the effects of the cocci until you can get the sulfadimethoxine, give the chicks milk orally via eyedropper. The milk will coat the intestinal lining slowing the effects of the cocci. You still have to treat them with a sulfa drug and sulfadimethoxine isnt as harsh on their system as other sulfa drugs. Do not give any nutrients or supplements to your chicks that contain thiamine, read the labels.
As for your brooders, they need need to be sanitized with an ammonia/water solution. Bleachwater wont kill cocci but ammonia water will take care of the cocci.