To answer your first question, I would be hesitant to say that there was a single leader as part of the conspiracy. While it wasn't solely concocted by the Pazzi family, they had of course a major role in the operation due to their own conflict with the Medici. Although if leaders had to be identified, I would cite Francesco Salviati as the main one, followed by both Francesco and Jacopo de Pazzi. But as I have said, there are numerous other players involved, such as Pope Sixtus IV, for example.

As for Assassin's Creed II, it has been a good few years since I've played the game, but I'll look up a list and label them as real or not real. If you want any expansion on them or your first question then just let me know and hopefully I can provide. To further preface, there was no Auditore da Firenze family.

• Leonardo da Vinci - real

• Rodrigo Borgia - real, served as Pope Alexander VI

• Paola - fiction

• Antonio de Magianis - fiction

• Rosa - fiction

• Uberto Alberti - fiction, although the Alberti were a major Florentine family and allies to the Medici

• Carlo Grimaldi - fiction, although the Grimaldi are a major dynasty and the current Monaco royalty are members of the House

• Lorenzo de Medici - real

• Giuliano de Medici - real

• Bartolomeo d'Alviano - real

• Jacopo de Pazzi - real

• Marco Barbarigo - real

• Silvio Barbarigo - fiction

• La Volpe - fiction

• Vieri de Pazzi - fiction

• Francesco de Pazzi - real

• Checco Orsi - fiction

• Teodora Contanto - fiction

• Caterina Sforza - real

• Niccolò Machiavelli - real

• Antonio Maffei - real

• Cristina Vespucci - fiction