There's 12 weapons here but 16-17 students (assuming John Danganronpa doesn't take someone's place).
I think that Fuyuhiko and Peko won't get a weapon because Peko is Fuyuhiko's "weapon" and Peko already has a katana. The Slayhem mode probably starts after the first trial.
#2x2
Idk about chapter 1-2. Chapter 3 Sonia convinces despair disease Gundam and Souda to die for her while also infected with the despair disease. Chapter 4 Nekomaru sacrifices himself for Akane. Chapter 5 everyone fucks up because they didn't listen to Nagito.