This is sounding a bit strange to me.....You say they are best friends, but it sounds to me like they haven't talked about you with each other at all. So what could be happening is.....girl one likes you as a friend only and so doesn't have to talk about how she feels about you with her bestfriend(girl 2).
OR girl 1 has talked about you with girl 2 (she may have said something like she likes you but wants to see what happens) and girl 2 has gotten jealous (can't find a better word) and decided she would flirt with you etc etc (trust me some bitchy girls will do that).
OR Both girls like you and haven't talked about you with each other (which may be because each one knows the other one likes you so they don't want to bring the conversation up).
OR I know there is more but I can't think right now.
Hope I haven't confused you, either way just talk to them.