Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

There seem to be mixed messages about this in the forum. What exactly does TWF do for Shield Bash? On the wiki it says:

Two Weapon Fighting, whether it has been selected as a feat or from an item, negates the -2 AB penalty when you turn Shield Bash on.

And also:

The Agile Shield Fighter and Two-Weapon Fighting feats can each negate up 2 from the penalty.

So a Shield Basher with a Tower Shield would get -4 AB with Shield Bash on for all attacks, right? With Agile Shield Fighter OR TWF, this would go down to -2 AB for all attacks, right? Now what if one took BOTH Agile Shield Fighter and TWF. From what I understood, this would remove the remaining -2 AB, but only for the Shield Bash attacks. Is this correct?

No, it's an "Or", not an "And". Taking both feats won't give you more than taking only one of those, as far as shield bashing is concerned.