First point : nothing prevents you from being engaged in melee against several opponents. Ok, not 12 of them, but 2 or 3 seems reasonable to me, allowing you to attack both of them.
Then, regarding Fiore Dei Liberi, in that case your second weapon is provided a statistic bonus to the first one (better damage and accuracy) but you only perform 1 attack. It's a "single attack with 2 weapons maneuver". As it is a single attack, you do not split your dice pool.