Firebellied toxins kill Red Eyeds--->Green Tree frogs die of stress of crowded tank--->Whites eat remaining Greens and toxic FBTs--->Whites die. Worse Case scenaro= happens in a period of a month or two. Best Case=happens a year later. Either way, it will happen.
If you want to try a mixed tank, try Greens and Grays. They are the only "acceptable" species capable of mixing. No others. Not trying to come down on you at all, just a warning. The animals wont live that long and thats a waste of lives and money. Just trying to help. 8-)