Quick question about the oldest son's death

I'm only vaguely familiar with the play, through reference books and the like, but I don't remember anything about the oldest son consensually hanging himself and his younger brother--let alone about hanging. In the play, at least what I know about it, it was all to be done 'off stage,' only the children's screams being heard.
Were these changes made by Dreyer or Trier? I know what the intro to the film says, but these changes just seem like a Trier move--Trier becoming Trier, so to speak.

(On another note, does it seem odd to anyone else that it should be Medea, a play about a woman seeking revenge, that Trier, given his more recent work, chose to adapt to film?)