How can I and my father can sell our Ancestral Property without my grandfather and his second son

I am 29 years old and I am the only child to my father who's 55 years and my grandfather is still alive and has one more son who has one daughter and a son. As per the division and rituals after the demise of my great grandfather my grandfather became karta and all the land (Ancestral property) got transferred or legally acquired by my grandfather and remained unsold and undivided in between my father and his brother. My father and I never took any benefits from earning or rent from entire properties. While my grandfather and his second son have taken advantage of entire source income from our Ancestral property. Now my father and I want to sell a part of our land and use the other few parts for business purposes and want to divide our equal rights with my grandfather and his second son and grandson. Our concern is we don't know how to sell our part without begging other heirs and how to seek our legal rights and legal or mutual division. The second son of my grandfather has clear intention of financial harassment to my father and delaying to gather for taking division decision and on other part my grand father flaunt all property as his own and only used for self income and profit of his second son. Please advise your best Big thanks and wishes