How many brothers? (also spoilers)

When Haewon first came to the island, Bok Nam introduced her to two guys - her husband and her husband's brother (the one who was always chewing Bozo leaf). So I thought it was just the two of them.

(spoilers) Then at the point of the daughter's death, I realize there are three brothers. I don't recall seeing the third one before - maybe he was a boat driver?

However, in the flashback scene, there are 4 brothers. By some of their facial expressions you can tell they are the younger versions of the men. So then I was expecting to see that one of the brother's was killed, but not.

So in the end, were there 4 brothers? And where was the 4th?