The African fat-tailed geckos tend to nip each others' toes and tails, but you can avoid this by always having a bowl of small mealworms available in their cage. Use a shallow bowl that the worms cannot get out of, and switch the uneaten mealworms daily so you'll always be offering mealworms that have recently had a meal. You should "gut load" a mealworm by fattening it up with nutritious food before you feed it to your fat-tail. Your reptile will be getting more bang-for-the-buck in his diet.
To learn more about this gecko, please read Choosing a Fat-Tailed Gecko