hello well there's always a chance of impaction with loose substrate, one way around this would be to feed in a separate container or to put in a feeding dish. you can house maybe even 3 in a 20 gallon long but it all depends on the geckos. You'll need to watch there behavior. if you do keep 2 females it's best to have 2 cool hides, 2 hot hides, and 2 moist hides. the best way to dust insects (in my opinion) is to use a zip-lock bag and to put dust in it and put the insects in and then to close it and shake it up.