You can prove in the court the sale deed is void as the seller himself obtained the title by fraud and fraud vitiates every transaction. Although according to Section 19 of the Indian Contract Act, 1872 the contract will be voidable at the option of the buyer. However, since the seller himself did not have the title he cannot transfer the interest in the property to some third party.
Here the seller has acted as an ostensible owner. The section 41 of the Transfer of property Act deals with the transfer of immovable property by ostensible owner. The word ostensible is described in the dictionary as apparent, stated or claimed but not necessarily true. In simple words ostensible owners appear to be an owner but they are not the true owner but the Act differentiates between a person who poses to be an owner to defraud the purchaser.
Further in this case, you can obtain your property by filing a suit under Section 5 of the Specific Relief Act, 1963. Section 5 of the Specific Relief Act, 1963, provides that a person entitled to the possession of an immovable property may recover it by filing a suit in the manner as provided under the Code of Civil Procedure. You can claim possession of the property based on your title as an owner.
The title deeds can be declared void under Section 34 of the Specific relief Act, 1963. Section 34 states that any person entitled to any legal character, or to any right as to any property, may institute a suit against any person denying, or interested to deny, his title to such character or right, and the court may in its discretion make therein a declaration that he is so entitled, and the plaintiff need not in such suit ask for any further relief.
I hope this helps to solve your query.