Gift Deed Validity

Hi Every One, My parents (joint owners) have gifted a property through a registered gift deed around 6 years back. I got the Katha transferred into my name and it is shown in the EC also. I have been paying the property tax also since then. Now both my parents (Donors) are dead now. But my brothers and sisters are asking for equal share of the property and have filed a case in the Civil court. Their claim is that the property under suit is purchased by my parents (Donors) by selling the ancestral property at my native and all of them are entitled for equal share of the property. In the gift deed it is mentioned that the property was purchased by self earned money and also that since my mother is taking care of them in their old age, they are gifting the property happily and without any force. My parents (Donors) have also mentioned in the gift deed that other sons and daughters do not have any right on this property. Please can somebody suggest me whether this gift deed can be cancelled. I require expert opinion from one and all. Thanks for your patience and answers.