So did they have a heat source previously? He is likely slow and lethargic and not eating a lot because he is too cold. They do need to be able to get to somewhere that's at least 85 degrees to warm up at that age, and he also needs to be able to get away from the heat, so if the heating pad is...
Sorry you lost one. What symptoms did it have before it passed? What are you feeding them?
How old is he? The raspiness may be due to his voice changing as he ages, and him being so subdued may be because he is alone now. I would get a friend for him ASAP, any breed you can find a duckling of...