Here is the light and outside pic of their setup.
Pics of the entire brooder and more pics of the chicks with the bald spots
Try cleaning out the brooder, make sure they have access to a full dish of feed (chick starter 18-20% protein) and water. If no access to dirt for dust bathing (outside), then provide them with a tub of dirt to dust bath.
Provide them with more space to prevent picking and piling. Keep their housing clean and give them access to dirt for bathing.Skin looks maybe a bit puffy. Birds feathers unkempt for their age (8wks).
Could be some picking going on. Space issues or even nutrition. Hard to know.
Make sure everyone is able to access food and that water is available to all.