I just want to make sure I read correctly that all 4 are in a 10 gallon? Or are just two in a 10 gallon?

To be honest, 10 gallons is the bare minimum for one ACF so water quality may be playing an issue here if they are all in the same tank.
Is it filtered? Any live plants? How often and how much water do you change with the water changes?

A balance of genetics (like Tony and ACF I have had in the past) and environment play a huge roll in the development of these frogs.