If you are going to have a crib in your house, I suggest a crib tent over
the crib.  This will keep the cats out.  If you will be using a Pack N Play
as a portable crib, they also come with tents that are designed for outdoor
use, but you could use that inside to keep the cats out.
Before the babies' first visit, bring something to your home that smells
like them, like a blanket or a onesie from each.  Let the cats smell it so
they get familiar with their scent.
While the babies are over, don't ignore the cats.  Make sure they are still
getting plenty of love and attention.  Don't freak if your cats sniff the
babies or approach, but always make sure interactions are supervised.
Chances are the cats will sniff them and ignore.

-Kelly