In my experience, adult females generally don't have much problems being introduced to babies or young'ins. In fact, we've trying to reduce the number of smaller cages at RLR, and by doing so, we've had to introduce a lot of females (adult and babies, some of the same bloodlines, some not) together. We haven't had one problem (we've done multiple cages of setups this way). I've actually found that we've had no problems with intros of females to other females at all. (Males, on the other hand... oy.)
As far as separating the females when one (or more) are pregnant, I recommend it. Moms like their own peace and quiet, and to be able to nest where they want and to be left alone. Leaving another female with a new mom who happens to be maternal can cause problems - fights over the babies, etc. I figure it's best not to risk any injuries to mom, the other female, or the babies.