1. IF GrandFather has expired and IF your Father is the only remaining Legal Heir of GrandFather, and IF there are no other Legal Heirs, THEN the case, by legal default, becomes legally infructuous and Father will be the sole legal heir and occupant of ALL the property of Grandfather.
2. It seems that your fathers case was not represented properly in court with the relevant documentary evidence of his payment /contribution of funds for the Land and for the House. IF there are no other legal heirs of Grandfather, THEN file declaration suit for the entire property.
3. IF there are other legal heirs of GrandFather, THEN contest it properly with documentary evidences & witnesses and you will get a favourable order.
Keep Smiling .... Hemant Agarwal