I find it's critical to get 2 women who actually like to double up.  I've seen some strange results when I've done the pairing and find out the 2 are apprehensive because they don't know each other or worse they don't like each other.

I'd suggest you find one of the two and ask who she likes to play together with.  If she's got a few partnes she's compatable with, then you look at those and see which one apeals to you to complete the package deal.

It's great to say "they're professionals, they should be able to act their way through it", and I'm sure some can.  But you've got better odds if they do click together.  Doesn't have to mean they are into each other erotically, just that they feel safe and compatable working with each other.