Gift deed appeared after 10 years of purchase a plot but was not mutated after the purchase

A plot of 1400spft bought by my father in 1996 but he did not mutated it then and we have the possession of the plot science than. The plot was bought from person X. But by 2017 when my father visited the circle office to mutate the plot, he surprised to know that the plot is already mutated with a gift deed registered in 2007. Which we were unaware until 2017. The gift deed is in the name of person X's sister in law. After few months my father passed away. I want to file a case now. My concerns are: 1. Does the duration of knowledge of the dispute matters in the court? It's been almost 4 and half years now that we are aware of this matter. 2. I noticed that the signs in our sale deed and the their gift deed does not match. 3. I have contacted that seller whether he gift the plot, he denied and has no knowledge of such activities. 4. Unfortunately due to many quarrel the opponent forcefully using a part of the plot as path. And demanding to negotiate upon surrendering the path for then. Although they already have a path to enter to their house though which a truck can enter direct from the main road. 5. What are the corners I should look out? 5.