Be sure the water chemistry is fine. It's not a good sign when a previously-aquatic newt takes to the land. This happened to me and it didn't have a happy ending, despite my attempts to feed him and coax him back into the water. I tried earthworms and wax worms. He barely ate. One day, he was back in the water, but deceased. I hope you have better luck. I've had my younger newts take to land periodically and be fine, but once adults, they shouldn't leave the water for an extended amount of time. I've also seen newts refuse to go into the water if stressed after a move or something. My original pair stayed on land for well over a month when we first got them.
I'm sorry, but I have to agree that I wouldn't mix species, as nice as the set-up is to observe. Besides the temperature differences, there seem to be too many instances of one species being eaten by the other.
Good luck,
Dana