Property related to muslim family

Hi,I have a very big and confusing questions related to a property which belongs to my aunty (my father’s first cousin). Family tree – Aunty, her husband, and their two sons (all deceased). All of them were NRI – American passport holders, and neither of their sons were married. Uncle and their second son passed away in the USA a long time ago. Aunty and her first son passed away in India last year. My Aunty has a house in Bangalore; she bought this 20 years ago, my family and I have been living in the same house ever since. My aunty used to stay here in her house for around eight months a year, and a few months in the USA. After my uncle's death, Aunty was asked to stay in her Bangalore house since she had mental health issues. Aunty and her husband Invited my dad and family to live/take care of the house. Hence, we came and were living in their house and taking care by paying the electricity bill, house maintenance, and Tax. The last year my Aunty, along with her elder son, came down to Bangalore to stay here to settle down in India. Aunty passed away after a few months from a heart attack and was buried here. He son was still living with us in India since he was not sure what to do with his life. His paternal side of the family came and spoke to him as to what he wants to do in life and if he would like to move in with them. My cousin said he wants to stay with my family since he trusted us and was comfortable with us. He was staying in my native, along with my parents.After a few months, he left our house without informing anyone of us. My dad filed an FIR for a missing person and informed the US Embassy as well, but we were not able to trace him since he left all of his belongs (phone, passport, clothes, etc) he only carried a small backpack with him. It had been more than a year, and his whereabouts were still unknown. We prayed and hoped that he would return safely. A week back Sub inspector from a different state reached out to us showing us his picture asking if we knew this dead person since he had his ATM card with him. As per their report, he was dead within 4 days since he left our house. CURRENT QUESTION: 1.The house which they own, who is the rightful owner now according to Islamic law? 2.We never had any intentions of cheating their family; hence, we never considered to make any lease agreement, rental agreement, or power of attorney. It was face value and trust our both families had for each other. 3.Aunty doesn’t have any WILL. 4.Aunty has a younger sister who lives in the USA with her family for 50 years. Uncle has relatives in India. 5.Now, how to safeguard the property? How can we live in the same house peacefully? Is it possible for us to own the house? 6.We don’t want some relative to come and claim the ownership and harass us. 7.We also have all the original documents and tax receipts of the house, which was given to us by them for safe keeping.