I don't think it's really that cut and dry in every case, that it's all in the eye of the beholder, and trust me, I usually loathe the idea of people filling in plot holes with their own imagination. But this movie was a little different for me, it left so many otherwise completely inexplicable actions by the main characters that it's almost as though the writers were leaving a trail of breadcrumbs; though I won't restate my entire take on the film and all the things that led me to that opinion, it's in another thread if you're interested. And I've read more than one critic's review that agrees with my take exactly, that the plot basically went from stranger did it, to dad did it, to mom did it, to Lily left in a car, so who really cares in the end?
But I agree that the plot really left enough room to drive a bus through parts of it, and from the negative critical reviews I've read, that was the biggest problem critics had with the film as well. Some also have suggested that there was an apparent disconnect between direction and screenplay, which was kind of my impression.
The highlight for me was Kidman and Weaving, I thought both of their performances were really fantastic but good acting can only take a film so far with such a disjointed story.

There are a lot of ambiguous scenes and dialogue, but without further clarification, it's impossible to know one way or the other.
An interpretation would depend on your own state of mind and character. Do you see perdition and bad, uncharitable things around you? If so, then your interpretation of events in the movie will also be for the worse.
Are you upbeat and a cheery person, do you see the good in things? If so, so will be your interpretation of ambiguities shown in the movie.
It is an intriguing movie, but it is playing with people's minds since it never gives enough facts for any definitive explanation of what has and is happening. Maybe it's like real life in that regard, but it makes for confusion and ultimately something unsatisfactory in the viewing experience.

I respectfully disagree, I think the clues are all there.

Well it's too bad the director didn't FILM his feelings then, because as viewers, none of us have much of any clue what is or is not going on it's possible to concoct any explanation we want, but nothing is substantiated by what is shown in the movie itself

Not if he knew that was something very horrendously terrible going on under his own roof but for whatever his reasons were, he felt powerless to stop.