Welcome Cam!
I have 4 gray tree frogs and I'm actually fairly new to them myself. Right now I have 3 in one 10 gallon aquarium, and 1 in another 10 gallon aquarium (3 are new so they are in quarantine right now) They prefer to be up high, so when I put them all together, they will either be in an upright 20 gallon tank or in an empty 35 gal hexagon tank that I have sitting around (tall tank)
They like branches and leaves, so make sure you have some of that going on. What kind of substrate are you using?