Hello Clovenpine, I am very appreciative you saved them. It was a responsible commendable thing to do.
I have some experience keeping goldfish for 37yrs. I don't consider my self an expert though. But----Here is what I would do. I am not an aquatic specialist. Just a goldfish keeper.
They may have swim bladder issues. I would only feed them once a day on commercial feed about the size of their eye. 8 to 12 hrs later I would give them some steamed broccoli or soak some romaine lettuce in boiling water for 2 minutes to soften up, cool it off and feed them small pieces of that to help clear them out. Give them some greens daily, if you can. De shelled peas would be a great addition once or twice a week. They can eat greens for about 5 minutes. Remove un eaten foods quickly as it could spoil their water.
I would use Prazi pro as a parasite med. Anyone who comes in my house has prazi pro or something similar no matter what. For parasites.
Further, if you didn't slowly acclimate them to your water they could just be adjusting to the ph difference. Just presenting some ideas here.
If the body of the fish seem bloated past the fish gills, look up how to use Epsom salt baths for them. It could help tremendously.
Don't combine salt with prazi pro at all. Please make sure media is rinsed thoroughly before using prazi pro for them.
Further, pet shops say clean the filter once a month, but in my experience, I clean the filters weekly in used aquarium water or de chlorinated tap water. It will help keep them very healthy without issues. I let algae grow on the back wall of my tank to let them snack on and it can good for their intestines. Keep up weekly water changes.
Please remember, there is many different ways to keep goldfish, but these methods have helped my goldfish live well, over a decade mostly.
Im not a professional or breeder just a goldfish keeper . I hope this helps you.