Thread:D. Cello/@comment-3096856-20111023155133/@comment-1153722-20111023214625

Both from the Encyclopedia Making Of:

Mario's confirmation as Grand Master, and indirectly also Machiavelli and Ezio: http://gyazo.com/dbef11a5cae09d5b75cd08808f20a5ef

Yusuf's confirmation as Grand Master: http://gyazo.com/be01f1502a4ef7b93f9700725d966ae9

These are from actual articles from the encyclopedia. They seem to be more reliable sources than Alex Amancio himself, especially since interviews have contradicted the game canon before (like Altaïr and Ezio turning out not to be related).