In registered property

Hello. Please can you help me. I am female, live in the UK, and I am one of 3 siblings. We are all estranged since my mother passed away & do not speak sadly.... My mother before she died, built a house in the Punjab on land my fathers family owned. My mother passed away 6 years ago. Since then my father has been letting his brother live in the house. He then told his brother to move out but the family kept the electricity & water account meters running on the house. My father has recently been admitted to a home with dementia and cannot take any action on the property, or make any decisions about himself. The care home/hospital now have full responsibility for his liberty. The property in India is not registered to anyone. My sister ( who also loves in the UK) is trying to sell the property to a relative who lives in the village nearby without registering it. I think she will sell for a small amount and let the relative register the house in their name. She wants to take any proceeds from that 'private sale' for herself and not pay myself anything. I want to register the property to myself and split the proceeds equally between my sister and brother. My questions are: 1) What should I do to prevent my sister selling to the relative? 2)What can my sister do to prevent my registering the house. 3) Once it is registered can my sister stop any sale? 4) If she can stop the sale what does she need to do?