I'm very sad to here of your loss.
From the sounds of it your newts may have parasites. you will have to treat them according to what kind of parasites they are. Try quarantining one of your thinning animals and check it's feces as often as possible. If they are not formed well it could be digestion trouble. This condition is also sometimes described as crash syndrome, when a newt seems healthy and established but thins even with regular feedings. What are you using as substate? The crossed hind feet could be a sign of gravel impaction. One of my C.Orientalis died a strangely similar sounding death and on close inspection, impation was the cause.
I hope you find the source of your problems and a remedy. My sincere condolences.