First of all why did you buy them having seen them so sick? It will spoil your reputation (sick fish in the shop) and risk an outbreak of diseases that could wipe out the other fish in the shop.
To me it's a waste of time and money trying to fix those fish. Even if you manage to save them, the same thing will happen again later. They are too far gone and look like runts too.
If it was me I would cull them without second thought.
No offends , just my opinion.
ron