Father's Property

Hello Sir


My father is building a property with his sister's son ,and he is handling all the construction work. and my father has also taken a loan from Bank of worth 15lakhs and he is paying my father's loan EMI amount every month. My father's sister's son is kind of psycho and shows his money power and persuades my father and my father is so dumb that he now listens to his suggestions whatever he says against my mom, elder brother. My father is totally against me , my elder brother and my mom and listens only to him. I am just worried because he might be doing this because of the property , because he already done that with many people and owns 4-5 houses. Can you please guide me with a proper way how to overcome and stop him


Thanks