War between Land property

This is our situation. My grandpa died without will. He has 4 children. My father is the eldest. Then my father died without will too. We live in one of the houses that my grandpa own. Our problem is the other sibling's of my father dont want to give the title to us. They say that we cant hold it coz it is still under the name of my grandpa. Then they told us that dont worry coz the house and the land our mine but i want to be sure. I will make a quit-claim paper. And they said they will sign but Is it a strong evidence incase my auntie's change their mind? Yung papel po ba na pinirmahan nila ay malakas ng ebedensya para di kami mapaalis kahit di namin hawak ang titulo ng lupa? Please help us.