I found this while I was trying to search for info regarding the two actresses' abilities in speaking English, it's from a forum
so I can't vouch for the veracity of the claims:
I'm more worried about the acting abilities of Fukushima Rila and Okamoto Tao, both are models and that doesn't mean they are good actresses. Rila has done a bit of acting work but Tao has what I know never acted.
I think they were cast because of their english ability (even though I think a Japanese actress could have learned english for the part heck Nakatani Miki and Kimura Yoshino both speak english)
So I guess they both speak English fluently and I guess the worry is their acting ability?