When I got Monty at 7 weeks old he was too small to eat anything other than fruit flies and the next size crix up from pinheads. I would have thought that Dubia nymphs would be too small. Even the fruit flies looked big in Monty's mouth to start with! Also, at birth, if the sacs don't break you can pick them up and drop them onto a branch where they will stick, rupture and free the baby.
Congrats on the babies. We are feeding fruit Flies to our babies although they are veiled's and Panthers I am sure they can eat the same. I would say dubia nyphm would be a little big. Good luck and keep us posted with pics glad to hear the one baby is fine. hope the others are just good fakers