I am going through something similar with my part timer. He comes one day a week and has been coming since March. He is having major problems transitioning. He's not bad at nap, he just won't eat or play by himself. Wants to be held all the time and won't play with the other dck.
Where do you have the kids napping? Separate rooms? If so I highly recommend a white noise machine. Use the white noise setting and it drowns out ALL noise. I have one in each of the nap bedrooms and one in the hallway. Its a very valuable purchase when you have a screecher!
Try that and maybe just try separating the screecher as much as you can?