Our grandfather is doing everything he can to get us out of the house! The House and lot is in our..?

deceased dad's name. I have already moved out 2 months ago because of this. And our grandfather has even complained to the city mayor that my sister has to get out of the house. My sister is a bit hesitant because we are the only sole heir to our dad. Although our dad has other illegitimate children (2 girls,aged 7 and 8) and we're currently taking care of them. Because the money that was used to build that house is ou grandfather's. And our dad signed a contract stating that he (our dad) will pay for the house until 2001,if not,monthly interests would be applied until the house has been paid in full. And until that time when the house has been fully paid, the house belongs to our grandfather. We have already spoken to a lawyer about this. But our grandfather is really doing everything he can to kick us out! He doesnt even need the house because he has his own. Correct me if i'm wrong, but arent debts considered Null if the person involved had already ped away? Please help :(