First thing I would do would be go and find a grower that has a good level of protein. I'm really surprised that Dumor will even sell such a lower protein feed as a grower, honestly. Even MG feeds (which I generally dislike) use 18% protein. Starter/growers are about 18-20% as well. That could well be part of their picking issue and part of the reason why they're falling prone to something.
Also, of course, please get them spaced out as soon as possible. Honestly, being from Texas, I'd replace the hay with the shavings. Heat and hay mildew spores added to its lack of absorbency combined with crowded birds = big problems. (I'm on the Gulf coast down here in Texas.)
Third, I'd make sure that there is en extra water station and that all have electrolytes in them for a while. Check the temps in the barn and use a mister (when using shavings) if necessary to keep temps down a bit. Check to make sure there are no dead spots where fans don't blow. I found that to be so in my barn when I was growing out turkey poults this year. I thought it was cool because where I stood it was awesome. When I went down to their level, knee high, it was hot as heck. Adjustments had to be made.
Make good and sure that everything is ultra clean while they're so close and hot. I'd suspect heat first and lowered immunity due to their feed and pecking. I'd also check alll your birds' weights and make sure none are light as hot birds eat less.
I wouldn't think that they need to be wormed yet as they've been in a barn not ranging, etc. I'd aim for four months unless they feel really light or have yellowish-green or frothy diarrhea.
I wish I could come help you get those babies into their new coop area. I suspect that and a change to a better protein level of feed will help. Let me know if you need help finding a feed brand out there. (Incidentally, as I mentioned before, I do NOT recommend MG though I've raised many birds on it - maybe because I've raised many on it.) Nutrena is an awesome brand - you get less waste of nutrition for each pound fed. Purina is always the standard. (Their brand now is "sun Fresh"). Bluebonnet makes a super bunch of feeds if you can get them up your way. In fact, I'd say it's one of the finest poultry feeds made as it contains kelp and even probiotics (yeast, and also bacterial fermentation products). I know someone who was using LoneStar and liked it. Whatever feed, make sure it's a good fresh smelling bag of feed, no cobwebs, no mothwebs, no holes, no dust or watermarks.
Hopefully this will help you stop losing babies. By the way, what ages are they again?
Thank for your thorough reply!