Mutual agreement problem. Civil suit filed.

My mother in her will equally divided one floor to both her daughters. However, it was mentioned that each party individually can sell off their share after mutual agreement. The sister however was not agreeing to sell off the complete floor even though the house was about to fall apart, nor was she ready to renovate the floor. Since the house was in pathetic condition, I sold off my share after proper procedure. The sale deed was legal. Now that sister has filed a suit on the new owner and me stating that this sale deed must be cancelled as "mutual agreement" did not happen. Since months the answers are being exchanged back n forth but no decision is being taken. The new owner before the suit was offering the sister money to buy the floor, to renovate etc. But she disagreed for god knows what reason. What will be the outcome? How much time will it take? Since the sale deed was legal is it possible to get out of this mess quicker? As we are mere spectators... the real issue can be handled by the new owner and sister mutually.