hi
i believe that thay are now clssifeid in the oophaga genus and not dendrobates,however i could be wrong.im sure someone more knowledgeable will pitch in.With regards to keeping the two of them together I wouldnt advise it as they may interbreed and they may have different needs,however as i said im no expert,and i cant really help you with the viv size as i've only got d.auratus and they're in an exo terra 60x45x60cm but they're a bit larger than your's.