We read testimonies of the Saints who were present to hear Brigham Young speak and to see and hear him take on the appearance and voice of Joseph Smith.
As a lead-in to this discussion, I made a time-line of events leading to the martydom (see photos at the end). It helped set the stage for discussing the possible options of who would serve as the next President.
As an activity (see photos below) I set up chairs for each current member of the First Presidency and Quorum of the Twelve Apostles. We walked through what will happen when President Monson passes away and what happens to his counselors, President Eyring and President Uchtdorf.
We moved the pictures to the appropriate chairs to show the seniority of each Apostle and discussed how a new President of the Church is called and how new Apostles are called.
Succession in the Presidency activity