David and Alice Brother and Sister?

Ha, I just posted on the relationship thread about this. I'm wondering if that lines up too since the movie leaves room for interpretation.

This is what I wrote on the Relationship thread.

That would make a great twist for an ending. The only problem is that the next scene you see Lila looking at another house and telling the agent that "...she will take it, its just like home..." or something like that. So it couldn't have anything to do with that particular house.

It says in TMC On Demand description that they are brother and sister.

"A divorcing couple's house is taken over by a deranged brother and sister."

We are lead to believe yes. As it is highly hinted at by the story she tells about David's children's book. It is never confirmed though.

I thought it was stated in the movie that they were indeed siblings. Maybe even twins? Which I thought was weird, because I thought she was about 35 and he was 25ish. But maybe that's because she was so outgoing and confident, whereas he was so shy and withdrawn. I found it strange that the movie never did tell us much about these two people. Suddenly they were gone and the movie ended. Which left us with a lot of questions about what was going on. I guess the movie was from the point of view of Alice and she never really knew who these people were...she just had to move on with her life never knowing.

I thought David and Lila were brother and sister. David did say to Alice that "she is a part of me" (re Lila).