Blocking and parrying with two weapons

Question

I've been mastering a game of MERP where my PCs didn't take much care about protecting themselves and attacked at full force each round, only subtracting the Defensive Bonus from their shields from the incoming attacks. But recently a player decided to be more careful and using part of his Offensive Bonus to block incoming damage (the rules state that before you declare your attack you can subtract part of the OB of your attack to increase your DB for the next attack you receive).
This is not a problem when the PC is using a shield (usually a +25DB) and a weapon, but one of them uses two weapons in combat and asked how it would work for him.
As MERP rules don't specify anything about the two weapon combat style (in fact we had to go to the rolemaster fantasy rules in order to make his character sheet) we had to check the rolemaster rulebook again and got confused in case he decides to block/parry. This is a extract of what rolemaster rules state about parrying:

A defender may parry one melee attack each combat round by switching any or all of his OB (with the melee weapon he is using) to DB.[...]
If a combatant elects to parry with a weapon with his entire OB, he receives the "shield" bonus for his weapon. These bonuses are listed on the Defensive Capabilities Table T-3.6 (p.214).

The table adds +5 when using full OB to parry.

And this is what rolemaster rules state about two weapon combat:

Parrying: The user must reduce both weapon OBs by the same amount (i.e., the amount of his parry). Against one opponent, the user increases his DB by the amount of his parry.

And, in order to make it more confusing, Shields & Weapons section says:

[...]In addition, when fighting with one or two weapons, one weapon may be used as a "shield", but may not be used for an attack in the same round.

The main difference between blocking and parrying is that I can only parry attacks from the enemy I'm facing and still attack but Blocking can be used for any incoming attack. So, what I've leart and I want to learn is:

When wielding two weapons I need to use both of them to parry and both of them would be affected by the decrease of OB. But how is my DB increased? The same amount I subtracted from each or the sum of them?

I remember having read the first option is right, but I can't find it anymore.
Why would I use a shield if a second weapon can be used as one? And what bonus would it have if I decided to do it so: the normal shield DB or the OB plus the additional bonus of using full OB?
When using Shield & Weapon can I use my weapon as a shield? Would it count as having two shields and sum the DB of both?

Answer 1

Quotes and references are from AL&CL ICE:1100 (RM2) Which bares the most resemblance to MERP and is what I use when I expand MERP beyond the base book.

* When wielding two weapons I need to use both of them to parry and both of them would be affected by the decrease of OB. But how is my DB increased? The same amount I subtracted from each or the sum of them?

p14, 5.1 Two One-Handed Weapons If an combantant uses part of his offensive bonus for parrying, he must decrease both his weapon OBs by that amount.

So DB is only increased by the amount you subtracted from each.

Example
Bob the Rogue is fighting with two short swords and is attacking Barry the Orc. Bob has 100 OB with a short sword which means he has 100 and 80 OB if he does full attacks as left/off hand use has a -20 OB penalty:

Left-Hand Use (5.2.10) As discussed in Section 5.1, a weapon used in the left hand receives a special -20 OB modification.

If Bob decides to parry 40 OB then he will gain 40 DB vs. Barry's attack and his OBs will be reduced to 60 and 40, good luck Bob!

* Why would I use a shield if a second weapon can be used as one? And what bonus would it have if I decided to do it so?

For four reasons:
Weapons cannot be used as shields against missile attacks, this is the most important reason!
Weapons have lower DB bonuses when used as shields (There's only one weapon really that's worth using as a shield (The Main Gauche) because it has +15 DB bonus, which means if you use it as a shield you gain +15 DB and can still make a full attack with your other weapon without penalty.
A Shield bonus counts against all attacks, for weapons this bonus is low and parrying is against only a single opponent and will reduce your main weapon OB; so as long as you're facing multiple opponents shields are usually the way to go.
Shields can be made of special materials, which will increase their defense bonus, weapons bonus do not add to this when used as shields, this is implied from the 8.2.6 "Defensive Modifications" table as it lists shields bonus as part of defensive modifications and for weapons it states.

Weapon Quality (5.2.4) Weapons remarkable in material, construction or workmanship may add a bonus to a combatants's OB.

DB is not mentioned, although this obviously gives you more OB to parry with if you want.
The shield bonus (p11 8.2.5) is 5 for all weapons except the Maine Gauche, which is 15.

* When using Shield and Weapon can I use my weapon as a shield? Would it count as having two shields and sum the DB of both?

Yes. If you really want to defend yourself, although you're almost certainly better off parrying instead!
So if you were fighting with a Maine Gauche (Shield bonus 15) and a Full Shield (Shield bonus 25) you could use the Maine Gauche as a shield and gain a total shield bonus of 40, watch out that they're not attacking from behind though!
The situation that this could be useful for is if you have taken so many penalties from hits damage, criticals, fatigue and so on that your characters OB ends up zero or less - in that case you can still use the shield bonus instead of parrying with a negative value!