Few things -
1. Both girls on period and ready to do CIP, DFK etc is itself a big task to find.
2. You can check the list of girls (even pornstars) in Euro escort website, see if they do duo and ask them to bring a friend. In that way they will be more comfortable with each other.
3. Not sure how many girls are ok to do BBFSCIP in Europe (even though they mention in the website the experience as PSE). Bes shot will be talking to PS.
4. If you can pull out in middle of orgasm and put it in the other one, take a bow from me. I can't even think if pulling out while having BBFS with a hot provider that's why I prefer a provider who offers BBFSCIP (not BBFS only).
5. If you can find reviews of the girl(s), then it's better as you don't know how the chemistry will play when 3 of you are together.
I have done threesome with non PS providers (in Mexico) and it was way cheaper (500$ for two girls and 3 hours). but this was with cover.