If you watched the movie, you certainly have been shocked by the end. I think them drinking the ashes of their brother symbolizes making him a part of their body. As the girls said in the movie, they don't always keep their promises so absorbing him in their body ( side note: I recall in some Asian cultures, there is the belief that if you eat/drink a part of an animal/other being (example: a cow's brain, testicles,...), you will be more intelligent/good in bed), he will always be with them.

What do you think of the end and of it's potential meaning?