There's no need to be concerned. Two big-eyed tree frogs in a 29 gallon tank is plenty of space for both. Make sure you have lots of branches and leaves so they can climb and hide.
BETF have two calls. One is more of a chirping sound, when a female is around. It sounds like GA... GA... GA... (that is what mine does a lot). They do have a warning territorial sound too, which sounds more like a barking dog.... RRRRR...GA. (That's the best I can do).
Either way, your frogs will be ok with the space they have.