1) it is your case that your grand parents were not of sound mind at time of execution of gift deed . you will have to prove that your grand parents were not of sound mind . you need certificate of medical experts who examined your grand parents in this regard .
2) you have to annex copy of gift deed in your suit if you are challenging the gift deed
3) if you have copy of title deeds of property which were in your grand parents name you can enclose them too