First off, I would suggest that you separate your remaining two corns immediately. Housing together of hatchlings really isn't recommended for a variety of reasons. And now that you have one snake dead, it just fuels my conviction of that even more. Its never too late to separate.
Like I said earlier, stress in snakes can exhibit itself in a variety of ways. Lack of eating, failure to thrive, disease/parasite transmission, or cannibalism. Snakes by nature are solitary creatures, and when we force them to live how we want them to live, they may have other intentions in mind. I would almost bet that if you were to give them each their own home, their feedings would perk up and they'd be totally different snakes.
Cheap temporary housing can be accomplished by utilizing plastic storage containers until you have the means to get better accomodations.
2-3 pinkies per feeding is overkill, imho. You
can feed a snake too much. It takes a while for snakes to digest their food since their cold blooded, so if you're in essence continually cramming food into them, you're going to end up with a snake that's not very healthy. They've spent most of their energy into digesting, rather than growing normally.
Most hatchlings should eat 1 appropriately sized item every 5-7 days. When they look like they can handle two, I usually just bump them up to the next sized food. By that age, they should be on at least large pinks if not small fuzzies. Not to mention, feeding multiples on such a short time frame of days is risking a regurge.
If they don't eat after the 5 day period, don't bug them with food on the 3rd day after that. As dumb as it sounds, you can actually stress them out with food to the point they're afraid of it. If they want to skip, let them skip. They're not going to die in the meantime. Most healthy hatchlings can survive a month or two without food. I've got a non-feeding hatchling right now that hatched the beginning of October and just now took its first pink yesterday. Sometimes they know bette than we do what they need. If they skip a feeding, offer food to them again the next time everyone else eats.
Your handling schedule sounds really good. Most new comers to the hobby stress the poor little things out by handling them every day. Which its good to see you have some restraint that even I lack at times.
Oh, I hate to always suggest this, but if you haven't bought it yet, please get a copy of "The Corn Snake Manual" (older version) or "Corn Snakes: The Comprehensive Owners Guide" (2005 edition). Both are written by Kathy Love and are THE source for information about everything cornsnakes. They can be found at most petstores, Amazon.com, or you can order an autographed copy from her website,
www.cornutopia.com.
I wish you the best of luck with your little ones. Hopefully its not too late for the others. =)