Sorry you are having problems....I'm not a KHA and without pictures it's hard to tell, but I'd try to catch the remaining 2 and give them a good salt bath, this will help kill some nasties. Also do some small water changes (30%), and add some Koizyme, it will help eliminate Aeromonas and Psuedomonas bactierias, which in excess can cause illness and ulcers in stressed fish. Just the fact that the fish were moved to a new pond, even if the water qualities are better they are stressed. If you have a picture, go to KoiVet and along with you ponds water quality parameters post your problems and someone there should be able to help you.