I don't think Akina's friends are fooled about her and Kaede.
I'm actually not sure about that. I mean, from what that one girl said and the way Akina acts, it wouldn't surprise me in the slightest. It also wouldn't surprise me if their was at least one pair amongst them.
At the same time, she did invite Akina to a mixer. That could have been a joke, or something hairbrained, judging from the other girl's reaction, but it's also possible that it was a legitimate offer and they haven't a clue.