From the bear facts that you have stated, when the property was purchased by your grandfather once again, upon his demise, whatever, share he may have at the time of his demise would be an ancestral property in the hands of his heirs. Secondly, you should also find out what was the source of funds that came to be used for the purchase of the property after the death of great grandfather. If there was sufficient nucleaous to show then the property would be considered to be an ancestral property. It is only after the position of law has changed upon the commencement of HIndu Succession Act, 1956 whereunder if there is a death of a co-parcener, his share, that would devolve on his heirs would cease to be an ancestral property. Hence, you will have to take in to consideration who died when.