Would Sarada have to kill Boruto to obtain the Mangekyou Sharingan? Say Sarada wants the Mangekyou Sharingan, would this mean she would have to kill Boruto?
She wouldn't have to kill anyone herself, she just needs to go through a traumatic event like seeing someone close to her die e.g. Boruto, Sakura, Sasuke, ...

I'm not sure how Madara got his Mangekyou Sharingan, but he didn't kill his brother himself. Izuna gave his eyes to Madara on his deathbed to awaken the eternal Mangekyou Sharingan.

From the Wikia:


  It is initially awakened by the trauma suffered from witnessing the death of someone close to the user. Uchiha has historically misunderstood these criteria as the user needing to be responsible for the person's death, and for that reason, they developed the practice of killing their closest friends in order to gain the Mangekyō Sharingan.