DON'T FLUSH HIM!

There's always a chance it will cure itself! My fish have never had red sores in my years of aquarium keeping, but they've suffered from other illnesses. Other aquarium hobbiest told me it was a lost cause to try to save them but miracously they pulled thru! Don't give up hope!

Like Karen said, explain to your father that it would cost less to save the fish you have than to buy a bunch of new fish.

In the meantime, do a 25% water change in the old tank if you haven't already. Don't change all the water at once--it will stress the fish out.

Good Luck with your parents and the fishies ~ keep us updated!