It is not possible to reply to a question on this Forum on the facts of the case, as examination of facts requires detailed study of the issues involved.
However, in brief, let me point out that if your grandfather has a decree of 1985, which is about 35 years old decree, and if it was not challenged in appeal, etc., at that time, it may not be possible for the defendants’ successors to now challenge that in appeal after such long delay. The limitation period to file appeal, etc., would have expired long back.
Secondly, filing a fresh case in the civil court (as you have mentioned) at this stage may also be not tenable in law, if the cause of action is the same. This is because a second suit is barred by the principle of res judicata (see, section 11 of the Civil Procedure Code) and moreover, it would have been barred by limitation too.
This reply is based only on the basis of limited facts mentioned in the question. You should consult some local lawyer by showing him all relevant documents, etc.
Dr. Ashok Dhamija is a New Delhi based Supreme Court Advocate and author of law books. Read more about him by clicking here. List of his Forum Replies. List of his other articles. List of his Quora Answers. List of his YouTube Videos.