I think your thread should have been titled "how much is too much chameleons in one cage"! As said above, those conditions are simply not suitable for your chameleons. You may have seen them like this in a pet store, but pet stores notoriously do everything wrong. They only need to keep them for a short period of time so they usually are not concerned with doing things wrong if the animals survive it. However in the long term none of them would survive, period.
Chameleons are solitary animals and easily stressed by just the sight of other chameleons, and your are having to basically live one on top of one another. If you continue to house them this way you are going to lose them from illness, stress or fighting. A 20g tank is too small for even one of these animals. They need a vertical cage, preferably not made of glass because they need lots of ventilation to avoid the buildup of dangerous mold or fungus. I use the 18wx18lx36h cages from diycages.com personally and they are great quality. I made my first cage, as many others have so you could look into that option for a quick fix that may (or may not be) less expensive. If you search on here for cages you can get an idea of some design options.
Your chams look to still be in good health so it's certainly not too late to get them on the right track. But if you don't do that soon you could cause irreversible damage. They're in an important stage of growing and need a lot of tlc to establish good bones to support the rest of their lives.
You need to read the blog posted above, or
this is a good one too. Gutloading is very important, as is supplementation with mineral powders, and even more important is UVB light. Most chameleon owners start off with a great amount of improvement to do in their setup and husbandry so don't feel like you're alone. You've come to the right place, please let us know if you have any questions about anything!
