Lehi now addresses Jacob specifically, but we should not assume that the address was meant only for Jacob. Lehi specifically states: "2 Nephi 2:30 I have spoken these few words unto you all, my sons, in the last days of my probation; and I have chosen the good part, according to the words of the prophet. And I have none other object save it be the everlasting welfare of your souls."
The discourse is directed to Jacob, but it is a convenience. It is a way Lehi can continue to teach his wayward sons important spiritual information without spending too much obvious time lecturing them, a tactic that while it might have been the real desire of father Lehi's heart, would have been too difficult for Laman and Lemuel to bear. They would have ceased listening (perhaps) had the lesson been directed to them, but might (just possibly) hear what was said to their brother, and learn from that.
Lehi clearly indicates Jacob's place in the family. He is the first born in the wilderness, and was a child through the long years of the deprivations of the wilderness. As one born to that life, Jacob did not know the Jerusalem nor the wealth which Laman and Lemuel could not forget. Though there are no details, Jacob must have been more of a follower and believer in his father, as Lehi indicates that he suffered under the hand of his brothers. This would have been more likely to occur if Jacob had sided with Lehi and Nephi.