Was Federico Auditore in training?
As the oldest brother and most likely to take up the mantle of Assassin after his father, I was wondering if Federico was possibly training under his father as an Assassin already. In canon, he probably wasn't, but it would be interesting if Ezio was being saved for a later time.
Federico (in the short time we got to see him) always seemed focused and enjoying life and his family without a care in the world. It's as if he already learned the lesson Altair and Ezio eventually found out (enjoy your life and those around you, for this is our only life). Also, during his execution in AC2, he is the only one that is calm. Giovanni is obviously frightened because his sons are about to be murdered for things they were not a part of. Petruccio is scared and confused; the most innocent of everyone involved. Federico? His face is plain. He's only doing slight struggles attempting to get free. He's most likely happy with his time with family and friends. Best to stop while you're ahead, maybe.
That focus and attitude in the face of death makes me wonder if he was in the know of his father's legacy for a while.
I like to think so.
Remember how casual Federico was in the fight at the beginning of the game also.
He might have worked alongside Ezio. Instead of Ezio being the best that ever lived, he would have been half of the best that ever lived. THAT'S how we could do co-op! 
It was kinda obvious.
Giovanni trained his eldest son in basic Assassin training, such as free-running, pick-pocketing (possibly), and hand-to-hand combat. However, I doubt that he led Federico know about his Assassin heritage, and even if he did, Federico would've probably told Ezio.
Yep. We learn this during Claudia's ritual to become an assassin in assassin's creed brotherhood. Like ezio says our father was here our uncle was here and our brother was here too. So like yeah he wasnt in training, he was already an assassin when he was killed
I love it when someone is inspired to join The Hidden Blade because they know the answer to an old question. gerund cleared up the meaning of "Oc-e-Non" in his first post and decided to stick around.
Welcome to the site, FireSpirit!
From one former lurker to another: welcome, FireSpirit!