Greater 2 weapon defense stacking?

[Dyntheos]

Does Greater two weapon defense stack with Two weapon defense, and Improved 2 weapon defense for a total of a +6 shield bonus?

The feats make no mention of it not being able to stack.

 

[drunkmoogle]

They all grant Shield bonuses. Same bonuses don't stack.

 

[Darklone]

And a +12 shield bonus while fighting defensively would be quite good

 

[Oscar carramiñana]

The two feats provide same bonus type they don't stack