My theory .... (spoiler)
..regarding the reason to why the family committed suicide (before i came to this board) was that their daughter was terminally ill. There is a scene where she rubs here itching stomach and this i interpreted as a sign of paraneoplasi, as she could have cancer.
THEY didnt want to live because their daughter was going to die. But i was wrong and reality was quite the opposite! They dint want THEIR DAUGHTER to outlive THEM.
The parents anguish is sooo subtle that you dont have a clue what is going on until late in the movie. I wasnt until flushed their money down the toilet that i started to suspect the dire fate that awaited them.