Refusing selling party,Registry of home at registrar's office.

Hello sir, My question goes like- 10 years back my father purchased a land for home (around 1/10 of a Beegha). At that time my father's financial condition was not that good so that he can register this land at registrar office. so both the party went to a lawyer and lawyer made a statement on stamp paper that my father can register this land when ever he wants and the selling party will co operate in that. so the stamp paper has agreement of selling party(3 brothers and their mom as their father died before) with their photograph and thumb impression. now my father is continuously asking them to get registered the land at registrar's office and they are refusing to do so and saying take your money back and give our land back to us. it has been around ten years and the cost of land became 5 times of what was at that time we are worried because some of the people are saying they may sell the land again cause it is not registered by the name of my father. seeking for your guidance. please guide us what to do Thanks in advance