I bought 2 8-week-old kittens 2 weeks ago. Suddenly they both won't eat or drink, they're stumbling & lethargic & have glassy eyes. They are not urinating or having bowel movements. I have used an eye dropper to give them water & Pedialyte, which they take willingly. These kittens have never been outside since I've had them.

Take them to the vet, ASAP.

I second AW's advice above! If the kittens are not urinating they are probably severely dehydrated, beyond the point where oral liquids will help. There could be dozens of possible causes, but they will die within the next day or so without help.