Common staircase issue was in family arrangement

Living in a ancestral house which is constructed by grandfather's father and partitioned among his son in which stairs and water tank are common which is half in our and half in other side which was for family arrangement, and side property was sold to another party not of family member and he begin to construct the half of that, this is only way to enter my home and half stairs are can't be used because it will become narrow, my father is expired a year ago i am living in that house for more than 20 years and feel harassment by these, stranger coming from that way because these stairs are for family and now new purchaser wants take half of that please help me how to use my rights for passage staicase of our home Please help