Ad aspera

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

That's not what I mean. Let's say you have two axes – accordingly, each of them has 5+300% (not 10-600) and deals double damage to the shield – that is, any of your attacks has these properties. Or you have two maces – it turns out that when attacking with two hands, you have two chances to stun due to the attack from each of the weapons, and both of these attacks pierce armor.
What about two daggers? The ability for a critical hit that stuns is obvious, but will both of them have +1 attack from the I ability?
And what about two swords? Does the double bonus to stats from the I ability of perception + dexterity apply? And is parrying no longer enhanced?

Or are all these meaningless speculations, because bonuses from the same weapon still don't stack, and it's assumed that you'll use different ones?