Specific to Bangalore, unfortunately that's not he case. I checked with Sub-registrar office via one of my contacts. Here's what I found.
If the land is jointly owned by myself and my wife, and we intend to provide GPA to her father to sell the land:
1) Stamp duty for my wife's GPA will be Rs 200/- (blood relative), but mine will be (~6% of the value of the land)/2. Because it is not a case of blood relative.
2) That amount cannot be adjusted when my father-in-law sells the land to actual buyer.
This seems very unusual. Can I get some advice please? I am open to professional help.