Good movie. Made sense to me.
A father who is drunk and does not take responsibility which would make his wife look for support from her son which would start complex web of lies.
The Child does not want to go to school and learns that he can avoid going to school and not be bullied if he plays crippled. His mother will surely let the kid does what he wants as long as he is around her. (One can say that the mother did not know but the fact that his kid is very close to her most of the time and she just could not notice he is abled might not be possible).
The daughter is bright but neglected by her mother(busy with work and her son) and father who is irresponsible but also seems to be avoiding any conflict with her (even after he sees the love letter, roses and chocolates in the restaurant).
The Sister in law is just tragic. A widow who only feels pity and sorry for herself and goes away one day because she felt too much like a burden.
Movie is literally a warning of what lies and abandonment of responsibility leads to. This is what happens, predators like that doctor, shaman and the old pervert and his son can do and exploit people in need.