Karnata people by nature have a great 'dna' of how to cheat, so your 'uncle' is no exception. He just misused the term of 'gift' by grand father; 'building on the land might be sone kutcha hose in the modern parlance, so builders would have advised him how to demolish the structure; and the 'gift' grants your uncle alienable right of the property, that way he sold to builders, (like builders handle re-development of buildings'), it is next to impossible for you now to prove 'fraud'; as you did not take action when he demolished the building on that land.
that way, i have seen a lot of such Bangalore properties are being handled knowingly or unknowingly. if you do with knowledge, God also cannot save you.
same tactics now Karnata govt has done in Covery water distribution to lower riparian states just flouting hon SC order, but anyway karnata govt might lose the battle as it even had the temerity to flout the SC interim order a sub judice order.
You are a normal citizen there in karnataka, there you have over clever peopleare there like your uncle. Problem is you have to see how much financial muscle you have to fight the protracted battle to prove your uncle 'defrauding idea'. If you have ability try and see if you can put up the fight.