Daughter in law harassing

Hello...pls if I can get legal advices on my queries. My brother passed away on 28th aug because of cardiac arrest. He was just 38 and it was the unbelievable shock of our life. We were still in grief while my sister in law's behaviour changed and everyday started having heated arguements with my parents. We can very well make out that it's her family influence and words she's speaking. 4 days back she took her son and went to her parents place. 1. Only income of my father is his pension. Can she stay at her parents place and demand money for her expenses. Is my father liable for all her expenses. 2. After she went, we moved our parents to younger brothers place. But with this grief also we do not want to uproot parents place and settle them anywhere. They want to go back to their own house. If they stay together, she might make any false allegations and always that mental torture is there. What legal papers they can make. 3. Flat agreement was in the name of my mother and my brother, but all installments are paid by my father. So while doing registration can it be in all 3 siblings name ? Please if someone can guide me through this.