I don't recall your earlier post so don't know if you mentioned it there or not, but are all three geckos in the same cage or separate? If in the same cage, I would separate them all into smaller cages, easier to monitor their food intake and overall health and lessens any rivalry.
All crested geckos do grow at different rates and some may be slow to gain weight. Your feeding habits seem fine, alternating with the CGD and crickets each night. If all other conditions are fine (temp, humidity, lots of cover and hides in the cage etc) they should start growing soon. Unless you are under feeding them, is there any left over CGD or crickets when you feed? If yes, then try increasing the amount of food you are offering. If there is leftover food, then it could be other problems slowing down growth.
The one thing that could be causing slow growth despite healthy eating, is parasites. Have you had any fecals done at all on these geckos? If not, I suggest getting a fresh sample from each gecko ( best way is to clean the cages completely and search for fresh droppings a few hours after they wake up and refrigerate it to take to the vet the following day, or check in the morning and take it to the vet that day or refrigerate till you are able to take it to the vet).