Hello and welcome! As for lots of plants, that is what we have. Our gecko is sometimes very hard to find, but very happy. As for sparse enclosures, one has to remember they like to live on dense trees and well planted grounds. More plants = more hiding spots = more safety in their minds.
Are these two used to being together? (Were they housed together before you took them home?) Some crested, even females, are very territorial and people have posted here before that they need to be separated for both to flourish. Just a thought. A cheap 10gallon can act as a baby/juvi house until you can get/afford a larger enclosure.
As for the food issue, we just went over this a few threads down and about once a month, read down the forum for more information, but here is something I posted recently:
"But in the meantime, you should really think about crested gecko diet (CGD) by T- Rex. The majority of owners swear by it. It is a complete food, all the vitamins, minerals, protein, fat, and fiber your little guy/gal needs. IMHO, the best way to raise a crested is offering CGD (mixed with babyfood initially if they don't partake of the straight diet.) and crickets for extra growth punch. After they reach adult, you can feed only CGD, but we still treat her to a few crickets every week. (Which is probably why she's a bit on the chubby side, but we're trying to fix that too.) I like CGD because it lasts 6 months open on the counter, you just mix with water each serving. I also don't like worrying about her calcium intake, whether the crickets undusted themselves before she caught them for instance."
You should feed in a shallow bowl, I use the small dishes intended for soy sauce for sushi. Baby food flavors such as peach, apricot, banana are well enjoyed, try to get organic if possible. Make sure water is available and that your temperatures aren't too hot or too cold. (Above 85F and below 60F)
Welcome to the world of cresteds! Good luck with your little ones!
-----
0.1 Albino Leo Gecko
0.1 Crested Gecko
1.0 Dear Boyfriend
Departed: Harvey and Spock