Begging for explanation/spoilers
I actually have some quetions about the plot because ist seems that there are even different interpretations about the plot
My idea:
Ewa was the daughter of Paul who now pretended to be Daniel (last group picture)?. Maybe he killed Daniel but I don't know the reason. That's very open to guesswork because Ewa does not identify Paul on the photo in front of the cop. Anna Mouglalis was actually Ewa (see pictures of the detective) and Magdalena Mielcarz was Milla.
A german view at the plot:
http://www.dieterwunderlich.de/Ando_preis_verlangens.htm#cont