Tough fish to keep. They arrive alive, but have (apparently) little resistance to poor water quality, high bacterial counts, and stress. As far as feeding? Easy: appropriately sized feeder fish or worms.
The best way to keep them would be in a well-planted tank, well-cycled, with low pH & GH, and alone.
I would advise against keeping them unless you are willing to dedicate a species specific tank for them. And if you already have one? Don't get too attached ...