DmD could use a total rewrite... That would be fun... My headcanon, and the only way that game works for me, is that week one, everything that happens from her arrival until the moment they reach the beachtown, zero sexual content. Though, I think I'd make it 3 full days before going to the beach town, you'll see why later. No massages, no exposed breasts, no on the lips kissing, none of it. A healthy father daughter reunion and a few days of spending purely platonic time together. We can fill the time with Elena seducing the ginger chick and stuff, just to get some action till then, but that's how I'd do that.
Then, on the beach, D asks MC to help with sunscreen, and he realizes he's excited by touching her body like this while also she realizes she likes being touched by him. It ends a little awkwardly when she moans a bit, and they both freak out, MC says, he's gonna go for drinks or something. Then when he comes back the scene where the guys are propositioning her is happening, so he gets them to leave, and she's given a reason to still trust him, even though they both have these new thoughts. Then that night, the dream where he sees her pleasuring him can cause that existential crisis and it has some weight.
Then later that day but before the dream and existential crisis I'd have them meet the other incest couple again, possibly by straying into the nude beach like before. Maybe they'd even catch them fucking... something to trigger the thoughts for D mostly, as I'd keep with the writing that skews her young, just I wouldn't make her completely naive anymore. A virgin, but not a complete childish angel of virtue. She'd hear the girl call out "Oh, Daddy, fuck me" or something like that, and the idea, much to her surprise won't disgust her. Then, they'd have startled the couple, ruining their moment, but being the charismatic dude that the father over there is, he'd come over to apologize that they saw that, and explain that they'd wandered onto the nude beach, that way we could keep using them to plant the seeds for D to think about it.
I'd have them trapped in the beach town for the rest of the week, rather than just 3 days. This would keep Elena out of the picture, and I could even find a reason that D didn't have her phone or something, maybe it got broken or something, so she uses MC's phone to contact Elena, because he had her number, and have her explain what happened to her mom. So that whole week, goes by, D and MC spending time alone together, sexual tension building, and finally, the night before they leave, the incest couple gives them their tickets to the dinner thing. Same as before, only now we've had a mature growth to their relationship over the last 5 days, all full of corruption of D's thoughts toward incest. None of that corruption coming from MC. In the end, it would be her who comes onto him. Her kisses, her touching... even if they don't go all the way there in the hotel, they'd get farther than a father and daughter should... The next day the nude beach would happen. Just like in the game, only since I've liberated D a lot, MC wouldn't have the drama over his trunks because he'd be nude.
They return home, and see Elena for the day, but D and MC have a date that night. However, unannounced to them, her mother comes to get her, similar situation to the game's ending. She can't get ahold of D because D's phone is still broken. Elena neglects to mention that she can get ahold of MC to give them more time. Meanwhile MC and D leave their date and D is once again all over MC, this night ends with them having sex. And here I put a huge choice, Cum inside or Pull out. No matter what you choose she's going home with her mom tomorrow before you can do anything about it. But If you do it adds a plot to part 2 where not only is D hiding her relationship with you, but the fact that she's pregnant. Drama and conflict for chapter 2 doesn't come from the relationship itself but from hiding it from their mom, and more importantly, if you came inside, what do do about this child. Does D want to abort? Does MC want her to keep it? All of that would be the kind of shit that's going on all while you're trying to get her back.