I had two Grays myself, and currently have a Green Tree Frog (american) that is very similar in care (just a bit warmer and humid than the Grays). I used to feed my guys 2-3 crickets every other night, but have since decided that with my new little guy, I'd rather give him a bit of a full belly than an empty one, and give him 3-4 now (dusted with Calcium+d3). I could also recommend tweezer feeding if you haven't attempted already, but that could still prove to be something they won't want to do until they are used to it, yet will help with managing feedings.