Regarding illegal occupying of ancestral property by Sister's Son

My grand father had earned all property and made houses and distributed property with registered will to all 4 sons and a Daughter. my father's house was given to my father's sister to stay because there her house was given to some government anganwadi school 20-22 years back . now that house is already empty and my father's sister is already passed away and her younger son is staying in my father's house. We are not taking any rent of that house. Father is paying all the property tax of that house till date. now they are not vacating my father's house and asking for money to leave the house. We are 2 sisters and my father is 72 years old now. Father's sister's Son is working in agriculture collage as senior professor and his 2 sons are also doing good business. the house is very old and in a poor condition butits located in central place in City so they all are taking undue advantage os papa and asking money to vacant our property. we had files a case under 133 in SDM for abolish the house as it is old and can cause any damage to the persons leaving in that house. Please advice me if we can get back my father's house without paying any money to them. will case filed under section 133 will help or we should go for some other way. thanks in advance.