Get a bigger viv. FBT's do well in groups and they are not at all expensive. They need some sort of water feature as well so even a ten gallon is kind of small for a group. I havent kept anything larger than these frogs in a 5 gallon and they were one to a viv. Full grown:
http://i948.photobucket.com/albums/a.../Retics007.jpg

You cant go too big with a viv.

Michael