Whose child is Juan

The youngest brother told the middle brother that the the oldest brother does not look like the mother or the father. Was he adopted or did he belong to someone else? Was he the wife's child but not the fathers. He was only left 10% of the shares, at first I thought he was the chairwoman's child?
But the chair woman said how old is son, who looked like his father who was his father?
Then the old man said he had traits like his father. I'm confused right now. This could be reason in a spoiler he doesn't want to get
Married