Grandfather Property Dispute Under Muslim Sunni Law

We are belong to Muslim Sunni Family My grandfather bought a property for living in the village Kasganj Patyali Uttar pardesh Grandfather died on 1988 without making any will after his death my grandmother was living there After some year grandmother wrote a vasiyat on my father’s name in around 2011 but unfortunately my father died before my grandmother death at 2016 but grandmother did not change the vasiyat and in 2017 she died My grandfather has 2 son and 3 daughters both son has died but all 3 daughter are married and alivemy grandfather elder son has 1 son (grandson) & younger son has 2 son (grandson) My Grandmother wrote the vasiyat in younger son which is my father Now my question is that 1. Who is legally heir of my grandfather property? 2. What is benefits of my grandmother vasiyat which is in my father name 3. Do we need all the member signature while selling the property 4. Can we both grandson change the ownership of our name without elder grandson if we don’t want to sell the property and give the property on rent 5. Under Muslim law how we will distribute the share and who is legally heirs for claim the shares 6. If we distribute the property so we will get double share one for my father’s name & other for my grandmother’s name because my grandmother also wrote her vasiyat my father name