How to sell property disputed between siblings?

Once an old man sell his property to his son and after few days of selling the property old man also make will of the same property in which he marked nominee to his daughter. His daughter filed case against her brother after receiving of same will after death of her father. Old man's son sell that property to my father. Even his son did not tell us about the dispute. The case was filed in the district court. After 8 years , district court puts the case in favour of old man's son. Now his daughter files case in the high Court. In which she said that she want some time for showing some more witness, due to which the case is now on hold from two years. We want to sell this property but due to their case we can't do anything. We can't able to sell that property and not can remodified the same. Please suggest us what we have to do.?? How can we overcome from this problem ?? What is the legal way to sort out this matter as soon as possible??