Glass cats absolutely need to be stocked in schools, but that can't be the cause of your issues here. You would notice excessive hiding and shyness, possibly problems feeding, maybe eventually death..but not in two days.
What are you water parameters?
How did you acclimate them?
If your nitrates are in check and your tank is free of ammonia and nitrites, and you acclimated them slowly by introducing small amounts of tank water at a time (or drip), then you will probably just have to call it bad stock. They could have been mishandled or had a rough time in shipment, can't say for sure.
I don't believe the remaining cloudy cats is a danger to your other fish, but I can't say for certain. It's a good idea to invest in quarantine set-up if you can, so you can observe new fish for a period of time before adding them to your display tank, and avoid the spread of disease.