welcome to the forums! how it works here is that you ask the question in appropriate section to get a faster and better response
but every single person here will tell you - NO to mixing species, especially firebellies and anybody else. they might appear fine for some time, but I'm wouldn't be too surprised if you come home one day only to find somebody dead or sick to the point nothing can be done. PLEASE for the sake of the frogs keep them separate. they all need different types of enclosures too.
moss is the last thing you want in a tank, unless you want to risk impaction that you are for sure facing.
check the corresponding section of the forum for more info on firebellies and tree frogs, there are tons of information and feel free to ask as many question as you need.