A person is threthening my family to vacate our home

We are staying in a property for somewhat like 50 years now. My grandfather was a teacher in a cni (chruch of north india) school and after his retirement my father joined the same institution in the same school. We have got this home as my family is serving the institution. But in the recent year a dispute has been going on between the mission (cni) through which this home was alloted to us with ucni (united chruch of north india). There is a person who called himself the property in-charge of (ucni). for past 1 month that person is calling my father and threatening my father that he will take legal actions and will call police and nagar nigam people to bring us out of our home. My father is still working in the institution. And is a kidney patient. He is not medically fit and for this past 1 month my family is going through mental stress. He even asked us to take our belongs out. Kindly, help me to know this better and what can be done in this matter. As my family is a middle-class and we are genuine part of the society never had any police case or something. We even had not take any legal step to the above mention matter. Kindly, help us.