Crested gecko question?

I have one, and the reason I have him is that he hared his cagemate so much she dropped her tail. So I would be worried that your 2 will not have enough space in a 20 gal and there will be stress and competition. That's a lot of plants/cage furniture for that size tank, you'll just have to arrange things to see how they fit--I have 2 pieces of driftwood, a vine, a live potted plant, 2 hides (warm and cool sides), and a food and water dish, and it barely fits. Plus the more stuff you have in there, the less you will see your cresties. They are nocturnal, so they start getting active once it starts getting dark. A great way to see them is to use a red light--doesn't disturb their activity but gives enough light that you can watch them. You'll have to regularly wash your repti carpet.... I've used it before, now I just use paper towels. I think your intentions are good I'm just not sure how it will work out--but again, you'll just have to play with the arrangement of things and see what fits, and then be very careful to monitor your 2 and be ready to separate them if needed, or perhaps a much larger tank. Good luck.