I think I figured out the ending?
Daughter lost her memories after crash and when she bumps her head they all came back. She's actually been in love with mc for a long time and had been finding ways to get with him like when he was drugged at the bar and realized it was her with him and she was in disguise but in her dreams she was misremembering/watching in third person rather than what actually happened. Mark is actually him and when she means exchange it was actually him she was going to see and this special thing she had planned on friday was to actually reveal to him everything. That is the reason she keeps mixing up Mark with the MC in her fantasies and dreams. All this unsureness from her and flirting and dreams were those feelings coming to surface despite the memory loss. Dad of course was always ingorant to it because everytime The Daughter made a move she did it when loading him with liquor or drugging him. Then when her and dad drink the spiked alcohol, they he is in horny mode while she gains a moment of clarity in memory and tell him how she feels.
There is also the possibility that they didnt actually crash like the daughter suggested and instead the vacation was on that island, and while its unknown how they got there or how they lost their memories, maybe the book will reveal that? Then my earlier statement still applies after this though. Maybe the Daughter used some kind of mental trickery or possible cult related magic to erase dads memory and the side effect is that it erased hers as well, and everything there she set up before hand to try and finally get together with the mc?
All those people who were in her dreams as well were trying to help her get the relationship with the mc that she wanted?
I can only guess the ending though because I am only assuming the mystery. For me, I could see a scenario where they aren't "rescued" for a long time and by then their relationship is so far along that even when rescued they stay together.
OR
The Daughters memories finally return and she realizes she got what she wanted and either chooses to stay on the island forever with the mc or escape with the mc having established the relationship she wanted all along, with a happy ending for herself. Maybe she even planned a way for them to disappear so no one could ever find them once they left the island so that they could live their relationship openly.
Only two guess I really have. I like to imagine a happy ending for these two coming from this. I seriously want to see the end of this one!