If Ramu had clear and marketable title to the property that he subsequently transferred to Ramya by a registered gift deed, then Ramya becomes an absolute owner of the said property by the virtue of the gift deed executed in her favor.
subsequently Ramya had transferred the property in the capacity of an absolute owner of the proeprty by executing a registered gift deed in favor of her son Rajiv.
Now by the virtue of the registered gift deed, Rajiv has become an absolute owner with clear and marketable title to the property now lying on his name.
Therefore in my opinion, since Rajiv has got perfect title to the property that you propose to purchaser from him, you may go ahead but before that to ascertain other facts and details you may better get a legal opinion from a local lawyer and proceed if recommended.