Hi Lyramon, welcome!
Well, bedding choices will definitely get you many differing opinions, as I am sure others will chime in soon about their picks for safe rat bedding!
The only no-no rules would be pine bedding which is irritating to ratty noses, but I am sure you already know that, and dusty beddings like sawdust, etc. Also inked newspaper is not a good choice of course.
Some people love Carefresh, but yes, I agree, it can be a bit too dusty. Carefresh Ultra is more expensive but much less dusty.
I know many people also swear by the pellet bedding like Yesterday's News or Aspen Supreme but you already said you are using that for your girls' potty tray. (I used Aspen Supreme pellets for my boys' potty tray actually and it was great).
My own choice for my two boys' bedding for the bottom of their house was actually using fresh towels and fleece blankies on the bottom of their house instead of loose bedding like Carefresh. BUT, when you do that, you need to do a lot of laundry!
I did about a jillion loads of ratty laundry (towels and blankets) every week as I pretty much changed their towel/fleece blankets just about every day or every other day, to keep it dry and not smelly. Zero dust problems with this method and very soft and comfy for the babies, but a lot of washing to do! I didn't mind doing extra laundry though.
Anyway, I am sure you will get LOTS of opinions on bedding! Hope I helped a bit! Looking forward to seeing pictures of your girls when you get them! I am sure you will fall in love with them.