Why is Zeke interested in Eren? In Attack on Titan's recent manga chapters, Zeke tells Eren that his father had lied to him and that he was unaware of the truth. Why is Zeke interested in Eren even when he can control titans and transform into one?
Update: This was further backed up by the events of chapter 87

What I think is that, according to latest manga chapter (86)


   Zeke and the other warriors are specifically trying to retake the coordinate from Grisha (and now Eren). He is also Eren's half brother (not step-brother) but it would appear that family is not an important bond to Zeke, as he betrayed both of his parents.