A-Chan is supposed to be faster than Mari but, well, why not, maybe it wasn't her day.
gronkle, this will not gonna happen unless Tôrajiro decide to end the manga, I think. And even if the manga end at some point, I'm not conviced that we'll see thoses girls fuck with each others. This is the point, the main line that even the title make it explicit.
This said, there is probably very few exceptions we can assume. First Ed and Ian obviously have an sexual life, but hey, they're older, there men and background characters, so, it doesn't count. Secondly and finally, we can also assume that Shizuka and Kaoru had sex before the time line of the first tome. Nothing sure though. But if it is the case, then we can expect Shizuka would like to go this far also with Ichinose (not to said that it's already te couple that gone the farthest).
Huge thanks to the Chads no teikoku.