BG2 Installed with,
'BG2 Fixpack' Core fixes and,
'BG2 Tweakpack' components of 'Rule Changes'
- Multi-Class Grandmastery (Weimer)
- True Grandmastery (Schumacher, Weimer)

Now, To the topic,

The concept of 'True Grand-mastery' only applies to Weapon Styles or even any single Weapon Proficiency?
1. For example,
Two handed Weapon style +
Two handed sword +++++

Here, 5/2 or 3/2 attacks per round still apply?
What about damage bonuses? +5 or +3?

2. Another example,
Two handed weapon style +++++
Two handed sword +

Here, True Grand-mastery bonuses apply when 2H Sword equipped or any other 2H style weapons like, Quarterstaff equipped?

Secondly, for missile weapons there is only weapon type proficiency with no weapon style.

Example:
Crossbow +++++
Number of Attacks: 3
To Hit: +1
Damage: +3

Here, To Hit and Damage Bonuses does not give a True Grand-mastery score of +5 damage.

My question is how exactly True Grandmastery works in BG2 for both melee and missile weapons??

True grandmastery doesn't affect weapon styles, you can't put 5 proficiency points into them. The Tweakpack has a readme:

You can't put 5 into styles?
But both styles and weapon(s) type have same descriptions than what are the differences? I think 2 weapon style allows 3.
I have never played BG1, the fixpack readme is a little confusing for me.

Weapon styles all allow 2 points, except two weapon style, which allows 3. It says as much in the creation screen. If you want to know what points get you what, read.

yeah..all right!.. read it a lot and that's not an issue but I'm no expert-person. I'd be happy and appreciate if someone gives me a nice info or link to weapon styles and proficiency of BG2 explained.
for example as the formula below,

(Base damage + Proficiency bonus + item bonuses etc) x backstabbing multiplyer + strength bonus ) x critical hit + additional weapon damage

Don't read the game manual and refer to online guides. I understand the confusion but not that difficult if you activate hit rolls to appear on screen.

Basically, Attack xxx 7 + 9 = 16 Hit includes every bonus and modifier in short. You will never know them in detail.

7 hit roll in d20 + 9 is the THAC0 (after all +/- modifiers) and 16 is the final Hit (not the damage)

Damage will be between 1-16 depending weapon type or any penalties and other immunities of the enemy.

One handed style = -2 AC and 1 critical hit on 19 or 20 (++ max allowed)
Two handed style = -2 speed critical hit on 19 or 20 (++ max allowed)
Two weapon style = No penalty on Primary weapon + reduces the penalty with the off hand weapon by -2 (+++ max allowed and -2 reserved for fighters only)

Basically manual never says that YOU can't raise pips in styles above 2 which was confusing to me at the beginning. Other than that there is nothing that difficult to understand.
Also, never ignore style on one weapon type as that gives better hit rolls even against strongest opponent.
By ignoring style you will have a lot of misses.

Any thing else ??