That's strange, I ran into that bug while play testing but we fixed it then. Seems other people are getting past it too. Of course with all the different ways you can go through the game it is possible for a bug to pop up. So you are just missing Paparazo the?
Not sure about the original poster for this, but the quest bugged out for me too, and I can list the likely reason why.
After seeing the mom in her yoga outfit I either (played for 5 hours or so yesterday so it's a bit fuzzy) immediately talked to her again and triggered something else, or went to sleep. I did get her naked on the toilet during this exchange too, but IIRC the shower thing happened immediately after the previous step, I did not have the MC go to sleep or do anything else first.
Not sure if that's the reason or not. I also only saw Melissa and Skye talking outside ONCE and then saw them changing, but cannot get the sister to mention mom having company, supposedly if you see her in the kitchen in the evening.
No idea how the flags are set for these but if they aren't all independant of each other, and the code check for parameters individually you may have things like this occur where part checks off and the rest of the quest doesn't, even if a specific scene plays.