I've never heard of pothos being poisonous to any frog. I've been using it for a couple of years with my Grey treefrogs and for 5 months or so with my Green treefrog (as long as I've had him and he's probably logged about 2 months of time on the Pothos). Pothos is sooo very common as a vivarium plant that I would be shocked to have not heard about problems with frogs by now. However, it is supposedly bad for cats (and maybe other pets) to eat, so maybe someone decided to expand this thought to include frogs?
You'll find most people here frown on multi-species tanks, and will suggest separate abodes for your frogs. However, as 3rd party anecdotal evidence I have seen a few reports of Greys and Greens being housed together successfully for many years. The decision is ultimately yours. (Note- mine are seperate as I don't feel I have the experience to tell if this is causing trouble). A definite worry though is their size- are yours close in size and all able to get their share of food?
Is there a water source they can sit in if needed?
How high is your tank? You mention getting a taller tank soon so that's good news

. I've found my green to stay at or near the top of the tank even more than my grays.
Finally, I don't find the colour disturbing. I have some pictures of mine in my album and the same frog will range from a very dark brown to a pale light green to a bright almost lime green. It pretty regularly changes from one to the other and as far as I know isn't any sign of distress.