Sorry to read about this and even sorrier that no-one's been able to provide any advice before now.
How is the situation now?
I have next-to-no experience/knowledge of ponds other than passing on some advice and useful weblinks to a relative who's currently helping out with a pond. However, on the basis of that very limited experience plus much more aquarium experience of goldfish, I wonder if feeding of vegetable matter (eg peas, courgette) might help to address what might be a buoyancy issue and perhaps flush through any undigested other food in their innards?
Let us know how the fish are now doing and perhaps one of us can advise further.