The viv is 45cm cube,do I needed to get a bigger viv, they also a phyllobates lugubris in with them.
I would keep the P. lugubris in the current viv and build something bigger for the D. auratus. 4 darts in a 45cm cube is a bit cramped, and Phyllobates tend to be bold and aggressive feeders, your auratus may have trouble competing for food.