Injection Suite

Hi My Father married two women in his life. While he was live he purchased few properties in the name of his first wife and himself. I am son on second wife. My Fathers first wife has a daughter. We all lived together happily with no issues. My Father expired in 2001. Later myself was taking care of both of my mothers and business. In 2009 i got my Sister(My Father's first Wife daighter) married and we gave all the dowry with gold and cash. My Father's first wife expired in 2016. Before 3 days of her expiration she gave a Registered Will to my mother making my mother to be owner of all the properties in her name and also any properties that are associated to my father. Now my sister and myself got some disputes. She has filed an injection suite claiming herself as owner of all the properties . Temporary Injection suite has been issues by the court. She had mentioned that the will is a created document and forged. However WILL is not a created document, it is Original and not forged. Can you let me know how can she(my sister) claim to be owner of the properties. However injection suite has been issued on my name and notice has been sent to myself only. Neither my mom got a notice nor her name is mentioned in the respondents.Can you let me know how can i defend\face this case against her. I need legal advise on how i need to proceed.