I don't see anything dramatically wrong with them in your pic. They don't have the look of Coccidiosis and I thought the "wet look" you describe could be poo on them but I don't see that either.... They look younger than 8 weeks maybe?? They're so cute! I assume they're in the corner because your phone scared them and not to get away from heat?? BUT it'd be really good to know what kind of temps that 250 watter is putting in there. I would urge you to ditch it altogether and if you have to provide light or heat (I don't know where your setup is or what the ambient room temp is,) downgrade to a 70watt bulb or anything you have that is way less heat. You said that one of the chicks that died hung out by himself in the corner and to me that means to get away from the heat. But again it'd be really good to know more about your setup. Inside? Outside? Temps where you are? Hang in there! They will be very pretty hens one day!! 
