Those are hard calls from photos. The spot is large to be ich, and looks more like he/she has cysts on the fin rays from injuries, or Epipstylis from poor conditions/poor overall health. Before you buy remedies, which may not work, try some aggressive maintenance.
So you're in the US, so I'll speak fahrenheit. The species should be kept at 82-85 degrees. It needs intensive water changing with equal temperature water, especially since you have 2 severely deformed, and therefore fragile fish. Any balloon fish is in constant health danger, especially for intestinal issues. They tend to have short lives compared to naturally shaped ones.
A lot of new aquarists buy them, and stores like their money, but the deformed fish have a lot of problems. It's possible you're simply discovering that.
