I'm so sorry you're going through this. Maybe double check their temperature with a different thermometer, in case the temperature is off. I know recently, someone posted that one thermometer read in the 80s and another one read 100 degrees. What temperature are you keeping them at? Other than that, it sounds like you have a good set up.
It can't be because of a batch of bad food or all your chicks should be effected. You've got them on pine shavings already? Did you start them on shavings right away or did you have them on paper towels for a few days? Could some of them have over eaten some of the shavings? How are their crops looking? That would be a lot of chicks to have that problem, though. Usually I think it's only a small percentage that might do that.
Were all of the chicks eating and drinking when you got them? Are the sick ones eating and drinking, now? Do you see them eat and drink? If not, you may need to nurse them, to make sure they are not wasting away. For chicks too weak to eat and drink, I use an eye dropper to put drops of sugar water on their beaks. I only do this if they aren't eating and drinking on their own.
Also, are you using a standard dosage of electrolytes? Maybe double check the dosage. One year a woman mixed the solution too strong and her chicks died from that. I don't normally use electrolytes, unless I'm treating diarreah, heat stress or dehydration. I do use sugar water if necessary to revive chicks that are weak from shipping, but after they are eating and drinking on their own, I go to plain water for chicks.
Have you called the person you got them from, yet? I would definitely call them. Is there any way this might be cocci, even without bloody poop? If so, there are meds for that. I don't know what else it could be. I've never had a problem with hatchery chicks having disease, but I've never gotten them from a 3rd party, either. I don't know what they could have been exposed to in those couple of days. Unlike basic care, I don't have personal experience with diseases. I hope you get more help from other people.