First off I agree with the commenters above, that the best outcome here is to release the animals back into the wild. I do appreciate that we are all a part of the WC trade, as all reptiles in captivity today have stemmed from WC stock, but both species are not uncommon in captivity, even as CB, so could be purchased more sustainably and responsibly whilst supporting those putting work into captive breeding these animals.
Regardless of the above, If I were you and were determined to either keep these animals or release them and purchase some CB from a breeder, I would not be looking at a 20gal tank. I would look at creating an outdoor enclosure, as large as I can manage, for them to live outdoors. Not only does that afford maximum space for the animals, but conditions will be pretty much perfect, less expense as you won't require additional heating/lighting, and whilst you will require some supplemental feeding, they will have access to wild inverts (dependant on how you set them up).