Oh tiny chicks!
Sorry for your losses
For tiny babies, I grind the feed down in a food processor for a week or so, this seems to help. I raise Quail too and they are like the tiniest little chicks so grinding feed to a powder or soaking it and offering it as a wet mash are easy ways to get food into them.
Pasty butt can a lot of times be from being too hot or too cold - go figure! It's up to you to determine which I guess. But if they are eating really well and drinking, it seems to help with the pasty butt too.
Are you using a heat plate or lamp? I like the plates better.
Hopefully you can get the pasty butt under control, after you clean the butt, apply a little coconut oil, triple antibiotic ointment or similar to the tissue, this will help soothe it and also helps keep the poop from sticking quite so bad.