Ad aspera

But does the accuracy bonus from swords stack up to a total of x3 when parrying?

No, each one provides the bonus only once. You won't get 10% Parry instead of five and 600% damage from two axes; parrying with swords will still be 1.5. And parrying won't change at all; it's still one roll and the same number of attempts per round.

Added 3 minutes later

Is there a way to unlock the Specialists somehow?

You can, but I wouldn't count on any specific ones. As I said, I'm considering giving 3 Attack Rating on the start.