بسم الله الرحمن الرحيم
A will made in favour of an heir shall only be valid when after the death of the testator all the heirs allow to implement it. In the above mentioned case it is understood from the question that the will of 80% which your grandfather made in your father’s name was not approved by other heirs (your uncle and aunts); hence this will which your grandfather made in your father’s name shall not be valid. After the death of your grandfather, all his property shall be divided among all his legitimate heirs according the Shariah in which all his four sons and daughters shall get their shares. Though your grandfather did not make a will to give share of your aunts, but due to this their shares shall not be cancelled. After your grandfather’s death, his daughters shall also have their shares in the property.
It should be noted that this ruling is applicable only when your father died after the death of your grandfather. In case your father died in the life of your grandfather then ask the question again.
قال الحصكفي: ولا لوارثه إلا بإجازة ورثته لقوله عليه السلام: لا وصية لوارث إلا أن يجيز الورثة – وقال الحصكفي: ولا تعتبر إجازتهم حال حياته أصلاً بل بعد وفاته – قال ابن عابدين: لأنها قبل ثبوت الحق لهم؛ لأن ثبوته عند الموت فكان لهم أن يردوه بعد وفاته (الدر المختار مع رد المحتار: 10/279، كتاب الوصايا، دار احياء التراث العربي، بيروت)
Allah knows Best!
Darul Uloom Deoband