I'm no expert and don't own Tree frogs, but from what I know a lot of the time the larger frog will bully the smaller frogs out of food. I suggest that you try and feed them separately or use a small glass bowl to place tiny crickets into so you can keep an eye on each frogs eating habits. The crickets can't grip the glass and therefore cannot escape making them easy pickings. I would try both methods.

I hope this helps