Yeah, they were said to be mother-daughter even before they made those videos together.
Edit: I think there is even a picture of Marina on the back cover of
ZEX-235, Moeha's AV debut. So she was advertised as Marina's daughter well before they even appeared in a video together. And if you look at Moeha's filmography, she hasn't done little else in JAV. I think she would not be in JAV if she wasn't really Marina's daughter. Her looks are not quite up to JAV standards. Even at 18 or 19, she pales in comparison to her middle-aged mother. I hate to be so mean, but it's the truth.