How long have you had them gakirby? This could easily account for them being shy.
They have many rocks to hide under as well as their piece of driftwood, so I don't think that is the case.
Try to create a dense 3D structure for them. This can be achieved by stacking loads of bogwood all the way to the top of the tank.
Panaque love this.
I am unaware as to whether or not they are wild caught except they seem kinda small to be from the wild. But the fact that they came together confused as one species must mean otherwise.
I would probably agree that they are wild. With long shipping distances it can take them a long time to settle down.
The tank water is currently 81-82 degrees Fahrenheit which according the the Cat-eLog is almost to their highest acceptable temperature. Should I go above this point to stimulate feeding.
If your water is very hard and alkaline it can take them longer to acclimate. Always check that your filter and pumps are working and up to the job.
Panaque produce huge amounts of waste, and if the filter is not up to the job, temporary ammonia spikes can put the fish off their food.
How would I know if they have these parasites? Should I treat for them as a precautionary measure? What is the risk if they end up not having parasites?
Not sure, but if everything else is ok, then parasites could well be the culprit. Are the bellies shrunken in?