Dead buff and sick one
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Your buff hen looks broody to me. Sometimes when I kick one out of the nesting box they just sit on the ground where I put them.
Have you checked them over for mites and lice? An overload can kill birds, and could be the reason why one is underweight.
Next, how much room do they have and what do you feed them? It looks like you have at least one feather picker. Feather picking can result from overcrowding, boredom, or a diet low in protein.