Property Issue

Hello Sir/Madam Family Details : Grandfather & GrandMother 4 Sons & 1 Daughter Grandsons & GrandDaughters Am one of the grandson of my family. My father is 3rd elder in his siblings. My grandfather & Grandmother are gov. employees, They both together built a 2 stair building, were their 4 sons & 1 daughter was raised and educated. Regarding sharing the property : Except my dad, everybody got their stuff (i.e. Cash, Property) My grandfather expired long back ago, 1year ago his 1st son also expired. Recently some issues raised against that 2 stair building. Issue : Grandfather wrote the property to his 1st son. (Brief Testimony) : "Am writing this testimony with good health and without any force. Except to my 1st son, I gave everything to my siblings. As am older and sick am taking this decision that, after my expire, this property goes to my 1st son. As because at present my 1st son is caring me and my wife and hope he will care us in future. My wife only has a right to live in the home. She don't has a rite to sell or transfer" Suspects : 1. Without any intimation to his wife or his siblings. My grandfather gave the property to his 1st son. 2. False Statement : He told he gave everything to all siblings. But he did not gave anything only to my father, regarding property or cash. 3. He told his 1st son is caring him and her wife, but its not true. My grandmother had a worst experience with his 1st son and his wife. 4. As that 2stair property was built together by grandmother and grandfather. Property was named under my grandfather. Do only my grandfather has a right on property? Then what was my grandmother role ? 5. Did that 2nd son forced/ unknowingly tried to make that testimony with my grandfather. Because my grandfather was severely ill at that time. 6. As 1st son has expired who has the right on property ? My grandmother wants a right on that property. So she can give to her grandson.