1. Any agreement of sale is legally valid for a maximum period of 3 years, unless agreed otherwise and has to have been recorded and agreed by both the Seller and the Buyer.
2. In the instant case, as per your narration, the agreement of sale was purported to have been executed way back in 2004 and the limitation comes into effect in 2007 and the 2004 agreement is legally not valid after 2007.
3. Assuming that your deceased father had executed an agreement of sale, the limitation bars the buyers from going for absolute sale of the property.
4. To be legally valid an agreement of sale should have been adequately stamped and registered in the Sub-Registrar's Office and the limitation time for it is maximum 3 years
5. It is your right to get copy of the Agreement from your relatives..
6. Reply suitably with facts to the legal notice and the law is in your side in the instant case.