Dual Weapon Attack and Parry

[Critical]

The context of this is a realistic game where dual weapon attack is allowed (but not the technique to buy it up). A character has ambidexterity, so both his weapons are at skill-4 when attacking with both simultaneously. My question is, does this affect his parry score? Does his parry drop down to (skill-4)/2 + 3 in a turn where he makes a dual weapon attack? If not, what if he's making a dual weapon attack but his opponent had a ready maneuver to strike at him as he's coming in for the attack?

I'm assuming that a character can hold two weapons and just attack with one at a time and suffer no penalties to attack or parry with either one. This is a major advantage as it allows two parries per turn before accruing any penalties for multiple parries. Is this correct?