There are multiple mother-daughter pairs in that movie???
Well, you are the better judge because I haven't watched that video yet and I can't understand Japanese anyways.
My view is, the concept of sister-sister and mother-daughter sex on screen is already far-fetched as it is, and to add more far-fetched elements such as bribery for good grades probably puts it into the realm of fantasy. Real sister-sister and mother-daughter sex is already as hot as can be, so embellishing it with drama would be unnecessary and maybe even detractive. Most JAVs avoid drama and embrace a documentary style for realism, and this movie does not do even that. So that's why I am sceptical.
Yes, there are several supposed pairs. All rather low-grade "hidden cam" with the same pixelated-face man too, it seems, who is some sort of schoolmaster or higher rank.
I don't understand Japanese, nor the culture. I agree with your reasons to be sceptical I think they must almost always apply. But we do know of a handful of videos where
sisters, and a mother-daughter or two, did something extreme for what, maybe 10,000 euro? Then I wonder if anyone would cross that line and do something extreme
for a few minutes if the daughter's graduation or promotion was at stake. I think we would agree there is no country where there is more pressure to do well in school. If
one googles topics about incest in Japan, many rumors and stories appear. Based on what I've read, if this could be real in any country it could be in Japan. I can only wonder.
Respectfully I must say I'm not sure about this video. I had expected another good fake. But in a way it's the uncertainty that strikes me. It doesn't seem a "smooth" production. The editing seems choppy and scenes short as if they didn't always have much to video work with. In one of the scenes the women keep clothes on and just give rather lame BJ's. Compared to other JAV it's not very good fare overall even as "hidden cam" goes.
Also yes JAV actresses are good at crying, but there is one where it seems sudden and real. Frankly it's rather disturbing, that. Perhaps they just fooled me. I think individuals will have to draw their own conclusions.