First thing I suggestion is house them in separate cages till both are eating fine and you know their sexes. A small plastic container with fake branches and leaves, papertowel for substrate and small feeding dishes and water dish is fine for young crested geckos.
For young crested geckos I find the ideal feeding dish are the plastic bottle caps off of 751ml bottles or smaller. Just pop out the plastic lining and drop about a quarter teaspoon of the crested gecko diet powder (mixed with water first of course), or babyfood (don't forget to mix a bit of multivitamin and calcium powder in with the baby food. Mixing a fruit babyfood and a meat babyfood (chicken, turkey, no fish) about one part meat, two parts fruit, pinch of multivitamin and calcium powder is good).
I feed on the ground, never had any problems with crested geckos feeding on the ground. However I do have ground cover as well, which may be why my crested geckos have no problem going to the ground to eat. Laying down a couple vine style fake plants on the bottom of the cage, certainly gives good ground cover. I use wooden dowels for climbing areas (leaning against the sides of the cage at an angle) with fake leafy plants propped up among the dowels and also fake vines wrapped around the dowels themselves.
For hatchling crested geckos up to about 3-4" in size, I house them in small dry storage bins I picked up at a dollar store. These are tall but narrow containers which are perfect for babies. One leafy plastic plant for climbing and hiding, and a fake moss bottom over a piece of paper towel gives nice ground cover and a relatively solid place to put the pop bottle caps, one with water, the other with food. I mist every day so if they don't drink moisture from the bottle cap, they can lick it off the sides of the cage. It also keeps humidity up. I drill some holes all around for air flow (else it can get moldy really fast in the containers with daily mistings).
For 4" or adult crested geckos I house them singly in 55L sterlite containers. These have the dowels for climbing areas and lots of fake plants.
Because small crested geckos do not eat alot of food, they could very well be eating the baby food you leave in. If you put in a fair bit, you won't see any eaten as they eat so little it doesn't make a difference on how much is left. Using small amounts in small containers, it is a bit easier to see 'tongue' depressions along the edges of the pool of food. Or for the food to be completely consumed.
Make sure your temps are good too, not too hot nor too cold. Temps should fall withing 70-80F with around 75F being best.
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PHLdyPayne