FatGiant I see your question... As regards Jaye, played through using supportive actions, didn't react when in the container, saved her from the sea but declined the bed fort. With Mallory did lay with her when she entered MC's room late at night and did engage fully with her at the beach. The reasoning being that I'd have definitely reacted very positively to her relationship-wise and I'd have also probably walked away due to teenage amorous feelings for Jaye as I'd have been scared that I couldn't control my feelings as too young. Now back and a bit older plus acting out the feelings in Sicily I'd really want a full on brother/sister relationship which wouldn't be possible if there was a full relationship.
However, the issues with Mallory are 1. that the MC seems to remember her but can't place where or why; 2. the taxi ride says she doesn't recognise Sarah in the MC but does in Mallory & 3. At the end the doctor tells Mallory that her test came back showing that she is Sarah. As regards 3 it's known that her Dad worked with Sarah and was besotted with her plus he mistreated Mallory as a child prior to his suicide as he thought that she was a mistake/freak & given that it turns out that he wasn't Mallory's dad and the lady she thought was her mum wasn't, the only conclusion I can reach is that she's a result of some experiment of his...
For me things go differently, not only from personal experience, but also from thinking about it for quite some time.
Jaye and the MC, you can opt to think about them has "brother/sister", they aren't, in my view they
know they aren't, probably 2 seconds after they ever felt a attraction for the other, if not even before... Theirs would never be a
normal sibling relationship, however hard they intended for it to be so. Where the taboo barriers would trigger for siblings, for them, there would be no such barrier.
Mallory, is even worse. She may be a clone of MC mother, but, she isn't his mother, she may share 50% of his DNA, but there are no real connections, except those that they make for themselves. Reproduction, well, that could be a problem. Anything else, is a normal relationship between 2 adults (or 3). The assumption that DNA determines behavior, isn't fully determined, AFAIK, the data available suggests impulse decisions are similar, but, decision making that requires a thought process, may or may not align. Nature vs Nurture arguments usually fall flat. I'll be waiting unabashedly interested where the authors take this. To me, there's no closed roads.
Anyway, nice to have a deep thought talk.