multiple tree frog species in same tank?

[Crunchy Frog]

You can't assume that they have the same toxins just because they're both hylids. As far as I know, no two species have the exact same toxins.

I had a Hyla cinerea once, a long, long time ago, and I currently have six juvie Hyla versicolors. In my experience, and from everything that I've read about their habitat preferences, I would not try to keep them together. Green Tree Frogs actually like to live in marshes and swamps, and I kept mine in a mostly aquatic environment (with a large potted plant, and a couple of good climbing branches). Grey Tree Frogs live in trees in forests, and only go to the water for breeding. In my experience, they need less water and lower humidity.

My Green Tree Frog did share his tank with a couple of aquatic newts (which are highly toxic) and, temporarily with a couple of bullfrog tadpoles/baby bullfrogs. This was nearly 30 years ago, though, and long before I knew about the importance of not mixing species. He lived for a few years, but eventually got sick and died. I have no idea whether the newts' toxins were a contributing factor. I would not try to mix species like that today, knowing what I now know.

My suggestion would be to decide on one species you would like to work with, learn everything you can about its natural habitat and requirements, and set them up with something that matches them as closely as possible, and then if you would like to work with the other species as well, do the same for them. I think that would be much more satisfying in the end.