Moving Callisto to the 30 gal (and the corn to the 20L?) is probably a good idea. It'll give her more room to grow, and you won't have to worry about upgrading her for a bit longer.
My '08s are pretty spread out along the scale. The smallest, Rhythm, is in a 12x12x12 inch. Asia (probably about the size of your corns) is in a 10 gallon. Greta (same size as Asia) and Hansel (almost twice the size of the girls) are in 20Ls... Xente, a small '05, is also in a 20L. All of them are comfortable in their tanks, but I intend to upgrade Asia before too long, so I can put Rhythm in her 10 and use Rhythm's 12x12x12 for a keeper hatchie (beauty snake if they're fertile, corn if not).
Yelina, another '05, is in a 29. She would be more comfortable if she could take advantage of the height... As it is, I'll likely be DYING to upgrade her once she gets her weight back up! She's fine at the moment, but she might get a spiffy 45 gallon or 40B after everyone who needs upgrades gets their upgrades.
Mallie, my '07 girl, is absolutely spoiled... She was my first snake, and even before I got my second snake she got to move from a 20L into a 36x18x18 inch Exo Terra.. A couple inches bigger in width and height than a 40B. She LOVES it, which is one of only two reasons I haven't moved Osiris into her viv and her into Osiris's 29 gal (the other reason being the huge almost-impossibility of properly disinfecting the gimungous branch and the foam background). I'd love to have all of my corns in one of those, but I don't have enough money to buy 6 more at $300 each..
Osiris is currently kept in a 29 gallon, which only works because she's tiny for her 2 years--about 30 inches and 670 grams. I'd like to upgrade her to a 4x2x2 ft enclosure, and then later to a 6 or 7x2x2 (depending on how big she gets), but finding either is a pain in the butt.. Especially since I'm holding out for a nice, wooden front-opening enclosure.
Jekyll is in a sparsely decorated 20H, at least until I'm sure he's nice, healthy, and firmly reestablished on f/t. When Osiris gets upgraded, he'll get her 29 gal... And when Osiris moves into her adult cage, he'll, once again, get her hand-me-down. =)
China, the '08 KSB (little 15 gram, 10 inch worm), is in the largest (and shortest) Faunarium available.. Not sure of the measurements--maybe 16x8x4 inches or thereabouts? Something like that! It almost seems TOO big for her, and if "she" is a "he", "he'll" probably be able to live in it his whole life. =)
Lucy, the 6.5 ft Taiwan Beauty, is currently living in a 75 gallon... While she could SO use something bigger, she's VERY happy with it.. She had been living in a 20H (actually, Jekyll's enclosure right now) when I got her, so the 75 is a major improvement. I think she's still getting used to being able to stretch out... And drag her rat 3 feet away from her water dish... Lol. =)
My "next snake" (assuming all goes well), a 10 year old Ball python, is currently living in a 45 gallon (not sure if it's regular [36x12x24] or long [48x12x19]). I believe BPs shouldn't be kept in anything smaller than a 40B, since they're considerably "big" snakes, no matter how lazy they are. "Hobbs" will likely get an upgrade, too, lol. He used to live in a 75 gallon, but the girl was having trouble controlling heat in it. My guess is the house isn't well heated--rural houses in this area aren't, usually.
Sorry that was so long... Lol!!
Anyway, as to what your snakes should be in. Your corns are perfectly fine where they are right now... The one in the 30 can be downgraded if you can't get a completely new enclosure for Callisto, and if you can get a new enclosure for Callisto, you can move the second corn up into the 20L... Then, both corns would be set for life.
For Callisto... The min. for an adult Colombian female is a 6x2x2 ft cage.. Probably 4x2x2 for an adult Hogg female, but finding specifics for the localities seems to be a pain in the butt... Lol. Depending on her percentage, she'll do well somewhere between those two sizes as an adult. You can get her adult-sized enclosure now, or get her an in-between... She will likely do well in the 20L (or 30 if you go that route) for a while, though. She sounds about the size of my Jekyll, who will likely be comfortable in his 20H for awhile if I can't upgrade him very soon.
