Sister's husband has no right in your parents property. Aside you held that your sister and her husband starts residing in your parent's house.... first of all the house belongs to her even (assuming there is no left behind will from your parents) and apart she is too residing with her husband, there is no problem and no law can stop them from this!!
For your right: - You also start living in that house. In case there is no room left for you, tactfully occupy a room and start residing there. In the mean time if you and your sister arrives a settlement, maintain that else file a suit for partition.