Daughter in law harassing father what action can I take

I am living in UK and working here. My mother passed away in 2009 and I have my father and he is an employee and retiring in few months and I am unmarried . I have an elder brother who is married and stays in our house (grandfather's registered) me and my father renovated as its old. My brother and my sister in law doesn't care or give him food and on top shouts, talks so low and hurts my dad for money. Therefore my dad started staying separately in small flat provided my Tata as he didn't want any argument, he eats outside everyday and is surviving on his own. My dad pays their bills too For past few months since my marriage discussions are going my brother and his wife started pressurizing my dad to write my grandfather property to their name. As I am away in UK and he is alone they are torturing my father and he is under pressure and doesn't know how to deal with this. We are scared that my sister in law would blackmail and as she is pregnant and take