The last story *SPOILERS*

So, did anyone else not understand the end of the last story?

So the mother killed her son...Does that mean she also killed her brother in the past? And what was the grandmother's role? She seemed to alternate between mad and sane. I couldn't piece together what was going on, particularly because it was a pretty boring movie and by the end I was having a hard time paying attention.

Any help would be greatly appreciated.