Well, I think I am beginning to sound like a broken record, but I sure could use some additional information from you regarding your three lizards in order to best help you. But, with the limited information that you have provided, I will try to help you as best I can.
You didn’t tell me the sex of your trio of geckos. Maybe that is because you don’t know, but it does matter. One male may be housed with two females, but two adult males should not be kept together, as males will fight with each other. Perhaps your trio has reached maturity and some territorial behaviors are beginning to occur. You didn’t say how old your lizards are or how long you have owned them.
It is fairly easy to sex leopard geckos. With three, it should be a simple matter of comparing the vent region and femoral pores, to separate the males from the females.
Cage temperature should range from 70-90 degrees Fahrenheit. They should have a hide box or cage decorations that allow them to hide from each other and from people too. A combination hide box and nest box can be fashioned out of a shallow plastic container with a hole cut in the side and then filled with 1-2 inches of moist vermiculite. This hide box will increase humidity in a small, dark area that will aid in shedding for lizards that otherwise need a dry environment, and it also provides an ideal area for females to lay their eggs.
Adult leopard geckos should be fed two to three times per week. Do you gut-load or dust the crickets that you offer to your lizards to increase the nutritional content? What type of substrate do you keep in their enclosure? Do you use sand, calcium carbonate sand, ground walnut shells or fine gravel? Some substrates can cause impaction if ingested (walnut shells, fine gravel or sand are more likely to cause gastrointestinal problems and impaction). It is always best to provide a varied diet to herps, and not get them used to eating just one or two insect types. The more the diet can be varied, the greater the chance that they will not develop nutritional deficiencies. Crickets, mealworms, waxworms, moths, flies, grasshoppers and other seasonal insects should all be offered for the best health of the reptiles.
Now, on to the causes of anorexia (the scientific term for not eating). Anorexia is not a disease in itself, but a symptom of something else. From the limited information that you have provided, I really cannot tell you much about why your geckos aren’t eating. It seems strange that all of a sudden two of your three geckos have stopped eating. If they are not gravid females (holding eggs), I think the best thing that you can do is to make an appointment with your herp vet to have the trio evaluated. Go over your husbandry and then pick up and examine each of your geckos for any signs of any external problems. If you have an accurate scale that can weight your lizards in grams, weigh them weekly. If they start losing weight, then you really need to have them seen by a herp vet. In the meantime, you can soak the ones that aren’t eating in a warm solution of clear sport’s drink (to allow them to drink and get some sugars, water and nutrients) in a shallow bowl for 20 minutes twice a day.
I hope this helps. Make sure that if they don’t start eating that you get them checked by a herp vet.