I don't believe they killed their brothers or Best Friends. What we see from Manga until now? Itachi didn't kill Shisui just saw it. They said Itachi killed him. Tobi was Madara, not him. Itachi showed to Sasuke these things and i don't believe He's " bad " guy like Orochimaru who could able to anything to anyone carelessly if he gain power. Madara and Hashirama shared same dreams, He's not a type of that guy kinda Sasuke, you know he couldn't kill Naruto either when he has a chance, They are in their own way/path. I believe they just died in front of his eyes, It's enough to awake MS too, like how Obito awakened his MS. Saw Rin's death. Still Hashirama & Madara & Obito & Naruto sharing same dream but in their way.