Hello and welcome to FF! Gail got you started well; most important thing now is that you read the linked care article and provide the proper enclosure heat parameter. White tree frogs won't do well if they can't bask on a 85F spot close to the light source. For that they will need branches or ledges to climb on. An 18x18x24 would be minimum size I would consider for one White female or maybe two males (they are smaller) since they are large frogs. If your 3 frogs turn out females; they will be crowded in there.

You can use a glass bowl to feed insects from. Insects should be gut loaded with fresh veggies (carrots, lettuce), veggie fish food flakes, and cherios or oats for 24-48 hours before feeding frogs. And if the little frog will fit inside the bigger frog's mouth, then need to keep separate because it could be eaten. Good luck !