Transit Camp Agreement Breach for over 28 years by the builder

Dear Sir, My name is R.K. & I am from Mumbai. I am seeking your advise on an unlawful situation that i have got trapped into. Twenty Eight (28) years ago, in the year 1987, my grandfather was made to enter into an agreement by the builder with his construction company, for moving into transit camp house for a period of two (2) years & get a One Room Kitchen (1RK) house in a building, in an exchange for a house in chawl. Few years later, the owner of the company - the builder died & his rights got transferred to his children, who are looking after for the company today. Three (3) years after this agreement was made, I lost my grandfather. This followed a loss of my father last year & I am the elder son in the family left behind with my mother & younger brother. And till date, for over 28 years the company & the present owners of the company have not fulfilled their promised 1RK & we are still living in the same inconvenient transit camp house. They are avoiding us & are not at all interested in having any talks on the subject in spite of repetitive follow ups for years after years. Even a letter local political authorities were unfruitful. We have lost all our patience & are unaware about how to tackle this matter having no legal knowledge. Hence, request you to please advise us on the same. Your advice is of immense value for us. We look forward to hearing from you. Thanks & Regards, RK