Your parents' contribution should be attributed to the loan contract. However, the contract has passed for more than 20 years. According to the provisions of the General Principles of the Civil Law on the limitation of action, the longest limitation of action shall not exceed 20 years, and the law no longer protects it. The money lent by your parents. It is probably impossible to get it back through litigation. This problem can be solved through private consultation.
After a hundred years, if the old man did not leave a will, the property will be inherited by your father and his brothers and sisters according to law.