How do you get to the point where the antagonist has the friend hypnotized and is harrasing the other girl in the dungeon with just the three of them? I've beaten the game and never saw those scenes.
If you're talking about the H-events that happen after
you beat the succubus... There's a couple of things you must do.
1st is to
not finish the dungeon in just one day. (which is entirely doable). Second is to specifically date Claire a couple of times, which opens Yuri up to be approached (and eventually fucked) by Leor. You'll have to then do a date with Yuri to really seal the deal. Once Yuri is Leor's fuck-buddy, it's
then that you want to send the three of them alone in the dungeon to start triggering the Claire events.
That said, before that, you may want to grab the "Just Yuri fell to the dick" ending.